Distance measuring apparatus

ABSTRACT

There is provided a distance measuring apparatus in lens-shutter type camera provided with a photographic lens, a focal length of the photographic lens being variable. The distance measuring device includes: a pair of image forming lenses each forming a subject image; a pair of line sensors on which the subject images are respectively formed through the pair of image forming lenses, the pair of line sensors each having a plurality of light receiving elements; a plurality of light receiving areas formed correspondingly on each of the pair of line sensors, the plurality of light receiving areas each including a predetermined number of the plurality of light receiving elements, wherein the plurality of light receiving areas respectively receive different areas of a corresponding one of the subject images formed through the pair of image forming lenses, and wherein each adjacent pair of light receiving areas of the plurality of light receiving areas overlap each other; means for detecting a current focal length of the photographic lens; and means for shifting at least one of the plurality of light receiving areas on each of the pair of line sensors in accordance with the current focal length detected by the detecting means, wherein each light receiving element included in the at least one of the plurality of light receiving areas shifted by the shifting means is used to convert received light into an electrical signal which is integrated to output image data.

This application is a division of U.S. patent application Ser. No.08/877,501, filed Jun. 17, 1997, now U.S. Pat. No. 5,923,910, which is acontinuation of U.S. patent application Ser. No. 08/605,759, filed Feb.22, 1996, now abandoned, the contents of which are herein expresslyincorporated by reference in their entireties.

This application relates to U.S. Pat. No. 5,051,767 (Date of Patent:Sep. 24, 1991), the disclosure of which in expressly incorporated hereinby reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a distance measuring apparatus, andmore particularly, to a passive distance measuring apparatus which doesnot emit light, such as infrared light, but instead utilizes ambientlight to measure a subject distance and which can be used in, forexample, a camera.

2. Description of Related Art

Some lens-shutter type cameras are provided with an autofocusing systemprovided with a passive distance measuring apparatus. This passivedistance measuring apparatus includes a pair of image forming lenses(i.e., distance measurement optical system) and a pair of line sensorsor light receiving sensors on which subject images are respectivelyformed through the pair of image forming lenses so as to calculate asubject distance based on triangulation. In cameras of this type, aphotographing optical system, a finder optical system and the distancemeasurement optical system are provided which are independent of eachother. In some cameras of this type, the distance measuring apparatus isconstructed as a single unit, i.e., a distance measuring unit consistingof the pair of image forming lenses, the pair of line sensors eachcomprised of an array of a large number of light receiving elements(i.e., photodiodes) on which a plurality of subject images of a commonsubject are projected, and an arithmetic operating portion forcalculating a subject distance based on triangulation in accordance withthe data outputted from the pair of line sensors. In the distancemeasuring unit, the optical axis of the distance measurement opticalsystem does not coincide with either the optical axis of thephotographing optical system nor the optical axis of the finder opticalsystem.

In conventional cameras of this type, in the case where thephotographing optical system is a zoom lens and the finder opticalsystem is a zoom finder whose magnification varies in accordance withthe varied focal length of the zoom lens, the relationship among thefinder view formed through the finder optical system, the AF frame whichis observed in the finder view and the distance measuring unit will nowbe described.

When zooming is effected towards the telephoto extremity, a subjectimage observed in the finder view is magnified due to a variation in themagnification of the zoom finder. However, the distance measuring unitalways receives on its pair of line sensors subject images of constantmagnification due to the magnification of the pair of image forminglenses of the distance measuring unit being fixed and not varied inaccordance with the varied focal length of either the zoom lens or thezoom finder, and furthermore, the size of the AF frame does not changein the finder view. Due to this, on the telephoto extremity side, thefocus measuring area indicated by the AF frame, superimposed on amagnified or close-up subject image in the finder view, becomes smallerthan the actual focus measuring area determined by the light receivingarea of each line sensor in the distance measuring unit.

Accordingly, there is a difference in size between the AF frame in thefinder view and the light receiving area of each line sensor in thedistance measuring unit. Due to this difference, in conventional camerasof this type, it is often the case that a subject, or subjects, observedout of the AF frame, but close to the AF frame are sometimes erroneouslybrought into focus through the distance measuring unit as a main subjector subjects, especially when the zoom lens is on the telephoto side. Asa result, the main subject is blurry in the resulting picture.

Furthermore, in conventional cameras of the type in which the opticalaxis of the distance measurement optical system of the distancemeasuring unit is not aligned with the optical axis of the photographingoptical system nor the finder optical system, the optical axis of thedistance measurement optical system in the distance measuring unit andthe optical axis of the photographing lens are not always arranged to beprecisely parallel to each other in an assembling process. If so, that acommon subject may not always be captured at the same time by both thedistance measuring optical system in the distance measuring unit, andthe photographing lens. It is not necessary to adjust the position ofthe distance measuring unit in the case where a deviation from anoptimum arrangement between the optical axis of the distance measurementoptical system in the distance measuring unit and the optical axis ofthe photographing lens is small, i.e., within an acceptable limit.However, if the deviation falls outside the acceptable limit, it isnecessary to adjust the distance measuring unit by moving or swinging itso that both the optical axes may be placed parallel to each other toeliminate the deviation. In an adjustment of this kind, the distancemeasuring unit is moved or swung mechanically relative to the camerabody.

After the distance measuring unit has been moved or swung foradjustment, data outputted from the distance measuring unit is checkedto find out if it corresponds to predetermined reference data. If thedata does not correspond to the reference data the distance measuringunit is readjusted. Therefore, the adjusting operation, in which thedistance measuring unit is firstly moved and data is subsequentlychecked, has to be repeated until such a time that the checked datacorresponds to the predetermined reference data, thus resulting in atroublesome, time consuming operation.

Furthermore, in conventional cameras where the camera has a macrophotographing mode for close-up photography which the optical axis ofthe distance measurement optical system of the distance measuring unitis not aligned with the optical axis of the photographing optical systemnor the finder optical system, such that the optical axis of thedistance measurement optical system of the distance measuring unitdeviates from that of the photographing lens by a large distance in leftand right directions of the camera, a deviation occurs between the twopositions. In other words, the position of a light receiving area on theline sensor on which subject images are projected in regular photographywhere a distance of subject located on the optical axis of thephotographing lens beyond a predetermined distance from the camera ismeasured, and another position of a light receiving area on the linesensor on which subject images are projected in macro photography for aclose-up where a distance of a subject close to the camera is measuredwithin a certain distance range. As a result, the AF frame in the finderview and the light receiving area of each line sensor of the distancemeasuring unit do not correspond to each other in macro photography,thereby the subject distance cannot be precisely measured.

In a known lens-shutter type camera which has an autofocusing systemprovided with a distance measuring apparatus including a pair of imageforming lenses, a pair of left and right line sensors each comprised ofan array of a large number of light receiving elements, used to define asingle light receiving area and an arithmetic operating portion forcalculating a subject distance based on triangulation in accordance withthe data outputted from the pair of line sensors, so that the subjectdistance can be calculated. However, in the measurement of the subjectdistance using one light receiving area at each line sensor, asmentioned above, there is only one measurement of the subject distanceto be effected, and hence, if no optimum value is obtained by the singlemeasurement or calculation, no focusing can be carried out, thus leadingto a missed photographic opportunity.

To solve this problem, it is also known to divide the light receivingelements of each line sensor into a plurality of blocks or groups (i.e.,a plurality of light receiving areas), so that the subject distance canbe calculated based on sensor data obtained from the pairs ofcorresponding light receiving areas of the line sensors. However, inthis solution, since a plurality of measurements obtained, based on thesensor data supplied from each pair of light receiving areas, arecompared to detect the largest value corresponding to the closestdistance, so that the focusing can be effected in accordance with thedetected largest value, the comparison operation must be carried out foreach measurement, contrary to a fast photographing operation.

In a conventional distance measuring apparatus in known cameras, thesubject light is split into two halves by a beam splitting opticalsystem. The two halves are converged onto, and received by, respectiveleft and right line sensors. Each line sensor respectively converts thereceived subject light into electrical image signals which are used forcalculation. Namely, for example, a correlativity (degree ofcoincidence) of the subject image data corresponding to the lightreceiving areas of the left and right line sensors is evaluated based onthe image data at different light receiving areas. When a high degree ofcoincidence is obtained, position data of the light receiving areascorresponding thereto is detected to calculate a distance between theleft and right subject images, based on the position data, andsubsequently, the subject distance is calculated, using the calculateddistance between the left and right subject images.

However, under conditions having a harmful influence, such as a backlitcondition, the amount of light to be received by the left line sensorcan be remarkably different from the amount of light to be received bythe right line sensor. If this difference occurs, the reference level ofimage data of the left line sensor (left image data) is different fromthat of the image data of the right line sensor (right image data), andhence the degree of coincidence decreases. Consequently, it is judgedthat the subject distance cannot be measured or the subject distance isincorrectly measured. In addition, it is difficult to distinguish theincorrect measurement from that caused by the existence of images ofsubjects at far and close distances in a light receiving area. Moreover,in some cases, even when a correct measurement has been obtained, theapparatus judges that no distance can be measured.

Furthermore, in a conventional distance measuring apparatus, if thecontrast of a subject is low, or if images of subjects at a closedistance and at a far distance coexist in a light receiving area, or inthe case of a succession of subjects having a repetitive pattern acrossthe light receiving area, no subject distance can be measured. Tominimize the occurrence of a subject distance not being able to bemeasured, a multiple measurement type distance measuring unit is knownin which subjects contained in a plurality of light receiving areas canbe measured.

However, in a conventional multiple measurement type distance measuringapparatus, the angle of view, i.e., the number of light receivingelements of each line sensor that are used to measure the subjectdistance for each light receiving area is fixed. If the angle of view islarge, i.e., the number of light receiving elements in each lightreceiving area is large, the subject can be measured in a wide range.Accordingly, the probability that no subject distance can be measuredfor a subject having a low contrast can be reduced, but the probabilitythat images of subjects at a close distance and at a far distancecoexist in a common light receiving area is increased. Conversely, ifthe angle of view is small, i.e., the number of light receiving elementsin each light receiving area is small, the probability that images ofsubjects at a close distance and at a far distance coexist in a commonlight receiving area is reduced, but the subject is measured in a narrowrange, and accordingly, the probability that no subject distance can bemeasured for a subject having a low contrast is increased.

Also, in the known multiple measurement type distance measuringapparatus mentioned above, one measurement which meets predeterminedrequirements is selected from a number of measurements. In an apparatusof this type, the reliability and validity of the measurements arejudged relying only upon a single predetermined reference level(judgement level). Namely, if the reference level (judgement level) ishigh, reliability is increased, but the probability that themeasurements do not meet the high reference level increases. Hence,there is likely to be a condition such that no subject distance can bemeasured. Conversely, if the reference level is low, reliability isreduced, thus resulting in an increase in the occurrence of incorrectmeasurements.

Moreover, in conventional cameras, it is necessary to measure rays oflight at a plurality of light receiving areas in order to judge whetherthere is a backlit state, through the functions of the camera. To thisend, it is necessary to provide a plurality of photosensors which detectrays in the light receiving areas or to use a split-type photosensor.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a passive distancemeasuring apparatus for a camera that can minimize the chances of thedistance of a subject, that a photographer does not intend tophotograph, being mistakenly measured as the distance of a main subject,in the case where the photographing lens of the camera is a variablefocal length lens or a zoom lens.

Another object of the present invention is to provide a passive distancemeasuring apparatus for a camera that makes it possible to simplify theadjusting operation in which the position of the optical axis of thedistance measurement optical system of the distance measuring unit isadjusted with respect to the position of the optical axis of thephotographing lens.

Yet another object of the present invention is to provide a passivedistance measuring apparatus for a camera that is capable of measuring asubject distance precisely in macro photography, in the case where theoptical axis of the distance measurement optical system of the distancemeasuring unit deviates from that of the photographing lens by a largedistance in left and right directions of the camera.

Yet another object of the present invention is to provide a passivedistance measuring apparatus for a camera in which not only can correctdistance measurement be carried out but also a subject distance can bedetected quickly, thus leading to a fast photographing operation.

Still another object of the present invention is to provide a passivedistance measuring apparatus in which an occurrence of a measurement notbeing able to be taken or of an incorrect measurement being taken, canbe reduced.

Another object of the present invention is to provide a passive distancemeasuring apparatus in which problems which would be caused when thecontrast of a subject is low or where there are images of subjects atboth a far distance and at a close distance in a common light receivingarea can be minimized.

Still another object of the present invention is to provide a multiplemeasurement type passive distance measuring apparatus which has a highreliability and in which an occurrence of a measurement not being ableto be taken tends not to occur.

Another object of the present invention is to provide a multiplemeasurement type distance measuring apparatus which can also be used asa backlit-state detecting apparatus.

To achieve the above first object mentioned above, according to thefirst aspect of the present invention, there is provided a distancemeasuring apparatus in a lens-shutter type camera provided with aphotographic lens, a focal length of the photographic lens beingvariable. The distance measuring device includes a pair of image forminglenses each forming a subject image, a pair of line sensors on which thesubject images are respectively formed through the pair of image forminglenses, the pair of line sensors each having a plurality of lightreceiving elements a plurality of light receiving areas formedcorrespondingly on each of the pair of line sensors. The plurality oflight receiving areas each include a predetermined number of theplurality of light receiving elements, wherein the plurality of lightreceiving areas respectively receive different areas of a correspondingone of the subject images formed through the pair of image forminglenses. Each adjacent pair of light receiving areas of the plurality oflight receiving areas overlap each other. The distance measuring unitalso includes a device for detecting a current focal length of thephotographic lens, and a device for shifting at least one of theplurality of light receiving areas on each of the pair of line sensorsin accordance with the current focal length detected by the detectingdevice. Each light receiving element included in the at least one of theplurality of light receiving areas shifted by the shifting device isused to convert received light into an electrical signal which isintegrated to output image data.

With this structure, the light receiving area on each of the pair ofline sensors can be varied or adjusted so as to correspond to a focusmeasuring area which is determined by an AF frame seen through thefinder provided in the camera. As a result, a subject(s) seen within theAF frame can be precisely and reliably focused. Furthermore, the chancesof the distance of a subject that a photographer does not intend tophotograph being mistakenly measured as the distance of a main subjectcan be greatly reduced.

Preferably, the pair of line sensors each has a size covering a maximumangle of view of the photographing lens.

Preferably, the distance measuring apparatus further includes a devicefor storing information of the current focal length detected by thedetecting device, the shifting device shifting the at least one of theplurality of light receiving areas in accordance with the information.

Preferably, the storing device stores the information in one of aplurality of sections in accordance with the length of the current focallength detected by the detecting device, the plurality of sectionscorresponding to a focal length variable range of the photographinglens.

Preferably, the shifting device shifts the at least one of the pluralityof light receiving areas in a manner such that the at least one of theplurality of light receiving areas approaches a corresponding center ofeach of the pair of line sensors as the current focal length detected bythe detecting device increases.

Preferably, the plurality of light receiving areas include a centerlight receiving area and at least two light receiving areas, the centerlight receiving area being located between the two light receivingareas, wherein the shifting device shifts the at least two lightreceiving areas in a manner such that the at least two light receivingareas approach a center of the center light receiving area as thecurrent focal length detected by the detecting device increases.

Preferably, the center light receiving area is fixed on each of the pairof line sensors.

Preferably, the shifting device includes a device for storing aplurality of predetermined positional data each representing a specificpattern of arrangement of the plurality of light receiving areas on eachof the pair of line sensors, wherein the shifting device selects one ofthe plurality of predetermined positional data in accordance with thecurrent focal length detected by the detecting device and shifts the atleast one of the plurality of light receiving areas on each of the pairof line sensors according to the selected one of the plurality ofpredetermined positional data.

According to the present invention, the photographic lens may be a zoomlens.

Preferably, each of the plurality of light receiving elements includes aphotodiode.

To achieve the second object mentioned above, according to a secondaspect of the present invention, there is provided a distance measuringapparatus in a lens-shutter type camera provided with a photographiclens, wherein a focal length of the photographic lens is variable. Thedistance measuring device includes: a distance measuring unit fixed to acamera body of the camera, the distance measuring unit including a pairof image forming lenses each forming a subject image and a pair of linesensors on which the subject images are respectively formed through thepair of image forming lenses, and the pair of line sensors each having aplurality of light receiving elements each capable of convertingreceived light into an electrical signal. The optical axes of the pairof image forming lenses are apart from an optical axis of thephotographic lens. The distance measuring device also includes a devicemeans for storing predetermined correction data corresponding to anamount of parallax occurring between the optical axes of the pair ofimage forming lenses and the optical axis of the photographic lens, adevice means for selecting a group of light receiving elements from theplurality of light receiving elements in accordance with thepredetermined correction data, only light receiving elements of thegroup being actuated to each generate the electrical signal, and adevice for calculating a subject distance value, using subject imagedata made by the electrical signals generated through the lightreceiving elements of the group.

With this structure, even if parallax of an unacceptable degree existsbetween the distance measuring unit and the photographic lens, a precisesubject distance measurement can be achieved through the distancemeasuring unit since only those light receiving elements on each of thepair of line sensors, which are selected by the selecting device inaccordance with the predetermined correction data, are used to generateelectrical signals which are used by the calculating device to calculatea subject distance value.

In other words, even if the distance measuring unit is fixed to thecamera body, a precise subject distance measurement can be achievedthrough the distance measuring unit even with parallax existing, withoutadjusting the distance measuring unit, i.e., by actually moving itrelative to the camera body, to reduce the influence of parallax. Thisis due to the fact that only those light receiving elements on each ofthe pair of line sensors, which are selected by the selecting means inaccordance with the predetermined correction data, are used to generateelectrical signals which are used by the calculating device to calculatea subject distance value.

The predetermined correction data is predetermined and stored in thestoring device during a manufacturing process.

Preferably, the predetermined correction data is stored in a memoryprovided in the camera. The memory may be a ROM.

Preferably, the distance measuring apparatus further includes aplurality of light receiving areas formed correspondingly on each of thepair of line sensors, the plurality of light receiving areas eachincluding a predetermined number of the plurality of light receivingelements, wherein the plurality of light receiving areas respectivelyreceive different areas of a corresponding one of the subject imagesformed through the pair of image forming lenses, and wherein theselecting means includes means for shifting each of the plurality oflight receiving areas in a common direction by an amount correspondingto the predetermined correction data. Further a plurality of lightreceiving elements which are included in the plurality of lightreceiving areas, once having been shifted by the shifting device, areused for generating the electrical signals.

Preferably, each adjacent pair of light receiving areas of the pluralityof light receiving areas overlap each other.

According to the present invention, the photographic lens may be a zoomlens.

To achieve the third object mentioned above, according to a third aspectof the present invention, there is provided a distance measuringapparatus in a lens-shutter type camera provided with a photographiclens, wherein a focal length of the photographic lens is variable, thecamera having a regular photography mode in which a subject locatedbeyond a predetermined distance from the camera is to be photographedand a macro photography mode in which a subject at a close distance tothe camera within a predetermined range is to be photographed. Thedistance measuring device includes a distance measuring unit fixed to acamera body of the camera which has a pair of image forming lenses eachforming a subject image and a pair of line sensors on which the subjectimages are respectively formed through the pair of image forming lenses.The pair of line sensors each has a plurality of light receivingelements each capable of converting received light into an electricalsignal, wherein optical axes of the pair of image forming lenses areapart from an optical axis of the photographic lens. The distancemeasuring apparatus also includes a device for storing predeterminedcorrection data corresponding to an amount of deviation between a firstgroup of light receiving elements of the plurality of light receivingelements, where a subject image of a subject located beyond thepredetermined distance being incident upon the first group in theregular photography mode, and a second group of light receiving elementsof the plurality of light receiving elements, where the subject imagebeing incident upon the second group in the macro photography mode, adevice for selecting a group of light receiving elements from theplurality of light receiving elements in accordance with thepredetermined correction data, only light receiving elements of thegroup being actuated to each generate the electrical signal, and adevice for calculating a subject distance value, using subject imagedata made by the electrical signals generated through the lightreceiving elements of the group.

With this structure, even if the parallax between the distance measuringunit and the photographic lens increases when in the macro photographymode, a precise subject distance measurement can still be carried outthrough the distance measuring unit since the first and second groups oflight receiving elements are selectively used in the regular photographymode and in the macro photography mode, respectively.

Preferably, the predetermined correction data is stored in a memoryprovided in the camera. The memory may be a ROM.

Preferably, the distance measuring apparatus further includes aplurality of light receiving areas formed correspondingly on each of thepair of line sensors, the plurality of light receiving areas eachincluding a predetermined number of the plurality of light receivingelements, wherein the plurality of light receiving areas respectivelyreceive different areas of a corresponding one of the subject imagesformed through the pair of image forming lenses. The selecting deviceincludes a device for shifting each of the plurality of light receivingareas in a common direction by an amount corresponding to thepredetermined correction data, and further wherein a plurality of lightreceiving elements included in the plurality of light receiving areas,having been shifted by the shifting device are used for generating theelectrical signals.

Preferably, each adjacent pair of light receiving areas of the pluralityof light receiving areas overlap each other.

Preferably, the photographic lens may be a zoom lens.

Preferably, the distance measuring apparatus further includes a devicefor switching from the regular photography mode to the macro photographymode, wherein the selecting device starts operating when the switchingdevice switches from the regular photography mode to the macrophotography mode.

To achieve the above fourth object mentioned above, according to thefourth aspect of the present invention, there is provided a distancemeasuring apparatus in a camera provided with a photographic lens,wherein a focal length of the photographic lens being variable. Thedistance measuring device includes a pair of image forming lenses eachforming a subject image, a pair of line sensors on which the subjectimages are respectively formed through the pair of image forming lenses,the pair of line sensors each having a plurality of light receivingelements each capable of converting received light into an electricalsignal, and a plurality of light receiving areas formed correspondinglyon each of the pair of line sensors, the plurality of light receivingareas each including a predetermined number of light receiving elementsof the plurality of light receiving elements. The plurality of lightreceiving areas respectively receive different areas of a correspondingone of the subject images formed through the pair of image forminglenses. Also included is a device for calculating, for each of theplurality of light receiving areas, a value corresponding to a subjectdistance, using the electrical signals generated through light receivingelements included in each of the plurality of light receiving areas, adevice means for judging whether or not there is reliability in each ofthe values in a predetermined order, and a device for deciding to adoptone of the values as an effective value, the one of the values beingfirstly judged by the judging device to have reliability.

With this structure, even if the value, for one light receiving area inthe plurality of light receiving areas, which is to be firstly judged bythe judging device is judged to be defective, another value of anotherlight receiving area is immediately adopted as an effective value in thefocusing operation. Accordingly, not only can correct focusing becarried out but also a subject distance value can be detected quickly,thus leading to a fast photographing operation.

Preferably, each adjacent pair of light receiving areas of the pluralityof light receiving areas overlap each other.

Preferably, the plurality of light receiving areas include first, secondand third light receiving areas, the first light receiving area beinglocated between the second and third light receiving areas at asubstantial center of each of the pair of line sensors, wherein the oneend and the other end of the first light receiving area overlap thefirst and second light receiving areas, respectively.

Preferably, the judging device judges whether or not there isreliability in the value of the first light receiving area, in the valueof the second light receiving area and in the value of the third lightreceiving area in respective order.

Preferably, the plurality of light receiving areas further includefourth and fifth light receiving areas which overlap the second andthird light receiving areas, respectively, wherein neither of the fourthor fifth light receiving area overlaps the center light receiving area.

The camera may have a Spot AF mode in which only the first, second andthird light receiving areas are selectively actuated and a Multi-AF modein which all the first, second, third, fourth and fifth light receivingareas are selectively actuated, wherein the distance measuring apparatusfurther includes a device for setting the Multi-AF mode or the Spot AFmode.

Preferably, the judging device judges whether or not there isreliability in the value of the first light receiving area, in the valueof the second light receiving area and in the value of the third lightreceiving area in respective order when the setting device sets the SpotAF mode, wherein the judging device judges whether or not each of thevalues of the first, second, third, fourth and fifth light receivingareas is reliable when the setting device sets the Multi-AF mode, andfurther wherein the deciding device adopts one of the values as aneffective value, the one of the values having been judged by the judgingdevice to have reliability and to be smaller or greater than any otherof the values.

According to the fourth aspect of the present invention, there may beprovided a distance measuring apparatus of a camera having a variablefocal length photographing lens, a Multi-AF mode and a Spot AF mode. Thedistance measuring apparatus includes a pair of image forming lenseseach forming a subject image, a pair of line sensors on which thesubject images are respectively formed through the pair of image forminglenses, the pair of line sensors each having a plurality of lightreceiving elements each capable of converting received light into anelectrical signal, and a plurality of light receiving areas formedcorrespondingly on each of the pair of line sensors, the plurality oflight receiving areas each including a predetermined number of lightreceiving elements of the plurality of light receiving elements. Theplurality of light receiving areas respectively receive different areasof a corresponding one of the subject images formed through the pair ofimage forming lenses. The apparatus also includes a device forcalculating, for each of the plurality of light receiving areas, a valuecorresponding to a subject distance, using the electrical signalsgenerated through light receiving elements included in each of theplurality of light receiving areas, a device for judging whether or notthere is reliability in each of the values in a predetermined order, anda device for deciding to adopt one of the values as an effective valuein the Spot AF mode, the one of the values having been firstly judged bythe judging means to have reliability. The camera may be a lens-shuttertype camera.

To achieve the above fifth object mentioned above, according to thefifth aspect of the present invention, there is provided a distancemeasuring apparatus which includes a pair of image forming lenses eachforming a subject image, and a pair of line sensors on which the subjectimages are respectively formed through the pair of image forming lenses.The pair of line sensors each have a plurality of light receivingelements each converting received light into an electrical signal whichis integrated to output image data for each of the plurality of lightreceiving elements, so that a group of image data is obtained for eachof the pair of line sensors, and wherein the image data contains atleast a brightness value. The apparatus further includes a device fordetecting specific image data from the group of image data for each ofthe pair of line sensors, the specific image data relating to a greatestbrightness value, and a device for calculating a difference between thegreatest brightness value for one of the pair of line sensors and thegreatest brightness value for the other of the pair of line sensors andfor correcting each of all the output image data in the group of imagedata of one of the pair of line sensors in accordance with thedifference.

With this structure, the image data of one of the line sensors can becorrected in accordance with the above calculated difference. Therefore,even if there is a considerable difference in the quantity of lightreceived by the line sensors, this difference can be absorbed orsubstantially cancelled, and hence, a precise distance measuringoperation can be achieved.

The output image data may correspond to a time value starting from amoment the electrical signal starts to be integrated until a moment anintegrated value of the electrical signal reaches a predetermined value,and the specific image data corresponds to a minimum time value in alltime values to which all image data of the group of image datacorrespond. In this case, the calculating and correcting device maysubtract the minimum time value at one of the line sensors from theminimum time value at the other of the line sensors to thereby obtain adifference therebetween. The calculating and correcting device furthersubtracts the difference from each of all the time values of the otherof the line sensors in the case where the difference is a positive valueor subtracts an absolute value of the difference from each of all thetime values of the one of the line sensors in the case where thedifference is a negative value.

Preferably, the distance measuring apparatus further includes a devicefor calculating a subject distance, using each of all the correctedoutput image data.

The detecting device, the calculating and correcting device and thecalculating device may be all provided in a single microcomputer.

The distance measuring apparatus may further include a distancemeasuring unit provided in a camera, the distance measuring unitincluding the pair of image forming lenses and the pair of line sensors.

The distance measuring apparatus may further include a plurality oflight receiving areas formed correspondingly on each of the pair of linesensors, the plurality of light receiving areas each including apredetermined number of light receiving elements of the plurality oflight receiving elements, wherein the plurality of light receiving areasrespectively receive different areas of a corresponding one of thesubject images formed through the pair of image forming lenses.

To achieve the above sixth object mentioned above, according to thesixth aspect of the present invention, there is provided a distancemeasuring apparatus which includes a pair of image forming lenses eachforming a subject image, and a pair of line sensors on which the subjectimages are respectively formed through the pair of image forming lenses.The pair of line sensors each have a plurality of light receivingelements each converting received light into an electrical signal whichis integrated to output image data. The apparatus also includes aplurality of light receiving areas formed correspondingly on each of thepair of line sensors, the plurality of light receiving areas eachincluding a predetermined number of light receiving elements of theplurality of light receiving elements, wherein the plurality of lightreceiving areas respectively receive different areas of a correspondingone of the subject images formed through the pair of image forminglenses, a device means for detecting a level of a contrast of image datafor each of the plurality of light receiving areas, the image data beingoutput from light receiving elements in each of the plurality of lightreceiving areas, and a device for adjusting a size of at least one ofthe plurality of light receiving areas in accordance with the detectedcontrast level.

With this structure, since the size of at least one of the plurality oflight receiving areas can be adjusted, i.e., enlarged or narrowed, inaccordance with the detected contrast level. If the contrast of asubject image is detected to be low, the chances of a subject imageexisting having a high contrast in the enlarged light receiving area areincreased in the case where the adjusting device enlarges the size of alight receiving area when the detected contrast level thereof is low.Therefore, the appropriate correlative evaluation data is obtained andthe possibility of obtaining an accurate subject image distance valueincreases.

In some cases a valid subject image distance value cannot be obtainedeven though the detected contrast of a subject image is high enough.This happens mainly because subject images at near distance and fardistance coexist within the same light receiving area. Even in such acase, with the above structure according to the sixth aspect of thepresent invention, the chances of obtaining a valid subject imagedistance value are increased in the case where the adjusting devicenarrows the size of a light receiving area when a valid subject imagedistance value cannot be obtained even though the detected contrastlevel of the subject image distance value in the light receiving area ishigh enough.

Preferably, the adjusting device enlarges the at least one of theplurality of light receiving areas in the case where the detectedcontrast level is lower than a predetermined level.

Preferably, the distance measuring apparatus further includes device forcalculating a subject image distance value, using the image data fromeach of the light receiving areas, wherein the adjusting device operatesonly when the calculated subject image distance value is valid.

Preferably, the adjusting device narrows the at least one of theplurality of light receiving areas in the case where the detectedcontrast level is equal to or higher than the predetermined level.

Preferably, each adjacent pair of light receiving areas of the pluralityof light receiving areas overlap each other.

The distance measuring apparatus may further include a distancemeasuring unit provided in a camera, the distance measuring unitincluding the pair of image forming lenses and the pair of line sensors.

According to the sixth aspect of the present invention, there may beprovided a distance measuring apparatus which includes a pair of imageforming lenses each forming a subject image, a pair of line sensors onwhich the subject images are respectively formed through the pair ofimage forming lenses, wherein the pair of line sensors each have aplurality of light receiving elements each converting received lightinto an electrical signal which is integrated to output image data, anda plurality of light receiving areas formed correspondingly on each ofthe pair of line sensors, the plurality of light receiving areas eachincluding a predetermined number of light receiving elements of theplurality of light receiving elements. The plurality of light receivingareas respectively receive different areas of a corresponding one of thesubject images formed through the pair of image forming lenses. Theapparatus further includes a device for detecting a correlativitybetween first image data output from light receiving elements in one ofthe plurality of light receiving areas on one of the pair of linesensors and second image data output from light receiving elements of acorresponding light receiving area on the other of the pair of linesensors, and a device for narrowing a size of both the one of theplurality of light receiving areas and the other of the plurality oflight receiving areas in the case where a degree of the correlativity isbelow a predetermined degree. With this structure, since the size ofcorresponding two light receiving areas are narrowed in the case where adegree of the correlativity therebetween is below a predetermineddegree, even if subject images at near distance and far distance coexistwithin a light receiving area or a subject image having a repetitivepattern exists within the light receiving area, the appropriatecorrelative evaluation data is obtained and the possibility of obtainingan accurate subject image distance value increases.

Preferably, each adjacent pair of light receiving areas of the pluralityof light receiving areas overlap each other.

The distance measuring apparatus may further include a distancemeasuring unit provided in a camera, the distance measuring unitincluding the pair of image forming lenses and the pair of line sensors.

To achieve the above seventh object mentioned above, according to theseventh aspect of the present invention, there is provided a distancemeasuring apparatus which includes a pair of image forming lenses eachforming a subject image, a pair of line sensors on which the subjectimages are respectively formed through the pair of image forming lenses,wherein the pair of line sensors each have a plurality of lightreceiving elements which convert received light into an electricalsignal which is integrated to output image data for each of theplurality of light receiving elements, and a plurality of lightreceiving areas formed correspondingly on each of the pair of linesensors, the plurality of light receiving areas each include apredetermined number of light receiving elements of the plurality oflight receiving elements. The plurality of light receiving areasrespectively receive different areas of a corresponding one of thesubject images formed through the pair of image forming lenses. Theapparatus further includes a device for calculating a distance value foreach of the plurality of light receiving areas in accordance with imagedata output from light receiving elements in the each of the pluralityof light receiving areas, and a device for judging, for each of theplurality of light receiving areas, whether or not image data isreliable. The image data output from the predetermined light receivingelements corresponds to each of the plurality of light receiving areas,wherein the judging device includes at least a first judging level and alower second judging level, and wherein the image data is firstly judgedat the first judging level and is then judged at the lower secondjudging level if none of the image data exceeds the first judging level.Also included and a device for selecting one of the distance valuescalculated by the calculating means, in accordance with respective imagedata, the respective image data having been judged by the judging meansto be reliable.

With this structure, the chances of having a focusing error occurringcan be greatly reduced while maintaining distance value reliabilitysince the image data is firstly judged at one judging level, i.e., thefirst judging level, then judged again at another lower judging level,i.e., the second judging level, if none of the image data exceeds thefirst judging level.

Preferably, the calculating device calculates each distance value inaccordance with first image data output from light receiving elements ofone of the plurality of light receiving areas on one of the pair of linesensors and second image data output from light receiving elements of acorresponding light receiving area on the other of the pair of linesensors.

Preferably, the distance value may corresponds to a distance between thefirst image data and the second image data.

The selected distance value may be greater than any other of thedistance values.

Preferably, the calculating device calculates correlative data betweenone of the plurality of light receiving areas on one of the pair of linesensors and a corresponding light receiving area on the other of thepair of line sensors by way of shifting, step by step, both of thecorresponding light receiving areas by a predetermined amount, andwherein the calculated correlative data is associated with the pluralityof different reference judging levels.

Preferably, each adjacent pair of light receiving areas of the pluralityof light receiving areas overlap each other.

The distance measuring apparatus may further include a distancemeasuring unit provided in a camera, the distance measuring unitincluding the pair of image forming lenses and the pair of line sensors.

To achieve the above eighth object mentioned above, according to theeighth aspect of the present invention, there is provided a distancemeasuring apparatus of a camera which includes a pair of image forminglenses each forming a subject image, a pair of line sensors on which thesubject images are respectively formed through the pair of image forminglenses, wherein the pair of line sensors each have a plurality of lightreceiving elements each converting received light into an electricalsignal representing a brightness value, so that subject distances ofdifferent areas of a common subject image can be measured in accordancewith the converted electrical signals. The apparatus also includes adevice for photometering an average brightness value of the commonsubject image, and device for judging whether or not a backlit-stateexists, wherein the judging device detects a maximum brightness valuefrom all the brightness values, calculates an average brightness valuefrom the brightness values for one of the pair of line sensors,calculates a first difference between the maximum brightness value andthe average brightness value, compares the first difference with a firstpredetermined reference value and judges that the backlit-state existsin the case where the first difference is greater than the firstpredetermined reference value.

With this structure, since the outputs, i.e., electrical signals, of thepair of line sensors can also be used for the judging device to judgewhether or not a backlit-state exists, it is no longer necessary toprovide a plurality of photosensors, a split-type photosensor or thelike used exclusively for detecting a backlit state.

Preferably, the judging device further calculates a sub-averagebrightness value from the brightness values for each of the differentareas, calculates a first difference between one of the sub-averagebrightness values and another of the sub-average brightness values, asecond difference between the one of the sub-average brightness valuesand still another of the sub-average brightness values and a thirddifference between the still another of the sub-average brightnessvalues and the another of the sub-average brightness values, selects anintermediate value from among absolute values of the first, second andthird differences, compares the intermediate value with a secondpredetermined reference value and judges that the backlit-state existsin the case where the intermediate value is greater than the secondpredetermined reference value.

The distance measuring apparatus may further include a distancemeasuring unit provided in a camera, the distance measuring unitincluding the pair of image forming lenses and the pair of line sensors.

According to the eighth aspect of the present invention, there may beprovided a camera having a distance measuring apparatus, wherein thedistance measuring apparatus includes a pair of image forming lenseseach forming a subject image, and a pair of line sensors on which thesubject images are respectively formed through the pair of image forminglenses. The pair of line sensors each have a plurality of lightreceiving elements each converting received light into an electricalsignal representing a brightness value, so that subject distances ofdifferent areas of a common subject image can be measured in accordancewith the converted electrical signals. The camera includes a device forphotometering an average brightness value of the common subject image,and a device for judging whether or not a backlit-state exists, whereinthe judging device detects a maximum brightness value from all thebrightness values, calculates an average brightness value from thebrightness values for one of the pair of line sensors, calculates afirst difference between the maximum brightness value and the averagebrightness value, compares the first difference with a firstpredetermined reference value and judges that the backlit-state existsin the case where the first difference is greater than the firstpredetermined reference value.

Preferably, the camera further includes a strobe, wherein the judgingdevice actuates the strobe to prepare for emitting light when judgingthat the backlit-state exists.

Preferably, the judging device corrects an aperture value in accordancewith the first difference when judging that the backlit-state exists.

Preferably, the judging device further calculates a sub-averagebrightness value of the brightness values for each of the differentareas, calculates a first difference between one of the sub-averagebrightness values and another of the sub-average brightness values, asecond difference between the one of the sub-average brightness valuesand still another of the sub-average brightness values and a thirddifference between the still another of the sub-average brightnessvalues and the another of the sub-average brightness values, selects anintermediate value from among absolute values of the first, second andthird differences, compares the intermediate value with a secondpredetermined reference value and judges that the backlit-state existsin the case where the intermediate value is greater than the secondpredetermined reference value.

Preferably, the camera may further include a strobe, wherein the judgingdevice actuates the strobe to prepare for emitting light when judgingthat the backlit-state exists.

Preferably, the judging device corrects an aperture value in accordancewith the first difference when judging that the backlit-state exists.

The camera may further include a distance measuring unit, the distancemeasuring unit including the pair of image forming lenses and the pairof line sensors.

The present disclosure relates to subject matter contained in Japanesepatent applications No. 7-34064 (filed on Feb. 22, 1995), No. 7-34065(filed on Feb. 22, 1995), No. 7-34066 (filed on Feb. 22, 1995), No.7-62254 (filed on Mar. 22, 1995), No. 7-87124 (filed on Apr. 12, 1995),No. 7-89645 (filed on Apr. 14, 1995), No. 7-128670 (filed on May 26,1995) and No. 7-128671 (filed on May 26, 1995) which are expresslyincorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in detail with reference to theaccompanying drawings, in which:

FIG. 1 is a front elevational view of a camera having a distancemeasuring apparatus according to a first, second, third or fourth aspectof the present invention;

FIG. 2 is a back view of the camera shown in FIG. 1;

FIG. 3 is a plan view of the camera shown in FIG. 1;

FIG. 4 is a block diagram of a control system of the camera shown inFIG. 1;

FIG. 5 is a schematic view of an internal structure of a distancemeasuring unit of the camera shown in FIG. 1;

FIG. 6 shows a general method for measuring a subject distance through apair of line sensors based on triangulation;

FIG. 7 is a schematic view of a distance measuring unit in the camerashown in FIGS. 1 through 3;

FIG. 8 is a schematic view showing light receiving areas of a linesensor used in the distance measuring unit shown in FIG. 7;

FIGS. 9A, B, C, and D represent a schematic view showing variations inthe light receiving areas according to a variation in the focal length;

FIG. 10 shows AF frames provided in the finder of an embodiment of acamera to which a distance measuring apparatus according to a firstaspect of the present invention is applied;

FIGS. 11, 12 and 13 are flow charts of the main operations of a camerato which a distance measuring apparatus according to the first, second,third or fourth embodiment of the present invention is applied;

FIGS. 14 and 15 are flow charts showing a "Photographing Operation"subroutine for a photographing operation in a camera to which a distancemeasuring apparatus according to the first aspect of the presentinvention is applied;

FIGS. 16 and 17 are flow charts showing a "Multi-AF Operation"subroutine for a Multi-AF operation in a camera to which a distancemeasuring apparatus according to the first, third or fourth aspect ofthe present invention is applied;

FIG. 18 shows AF frames provided in the finder of an embodiment of acamera to which a distance measuring apparatus according to the second,third or fourth aspect of the present invention is applied;

FIG. 19 is a schematic view showing a deviation of an optical axis ofthe distance measurement optical system of the distance measuring unitin a camera to which a distance measuring apparatus according to asecond aspect of the present invention is applied;

FIG. 20 is a diagram of output data of a distance measuring unit whenthe optical axis of the distance measurement optical system of thedistance measuring unit is deviated from a reference optical axis in thecamera shown in FIG. 19;

FIGS. 21A and B show a line sensor having additional light receivingelements corresponding to a maximum parallax adjusting amount in thecamera shown in FIG. 19;

FIG. 22 is a flow chart showing a "Photographing Operation" subroutinefor a photographing operation in a camera to which a distance measuringapparatus according to the second or fourth aspect of the presentinvention is applied;

FIG. 23 is a flow chart showing a "Subject Distance Measuring Operation"subroutine for a camera to which a distance measuring apparatusaccording to the second aspect of the present invention is applied;

FIG. 24 is a flow chart showing a "Multi-AF Operation" subroutine for aMulti-AF operation in a camera to which a distance measuring apparatusaccording to the second aspect of the present invention is applied;

FIG. 25 is a flow chart showing a "Spot AF" subroutine for a spot AFoperation in a camera to which a distance measuring apparatus accordingto the second aspect of the present invention is applied;

FIG. 26 is a schematic view showing a deviation of an optical axis of adistance measuring unit in a camera to which a distance measuringapparatus according to the third aspect of the present invention isapplied, in a macro photographing mode;

FIG. 27 is a diagram of output data of a distance measuring unit in anormal photographing mode and in a macro photographing mode in thecamera shown in FIG. 26;

FIG. 28 is a conceptual view of light receiving areas when in a macrophotographing mode in the camera shown in FIG. 26;

FIG. 29 is a flow chart showing a "Photographing Operation" subroutinefor a photographing operation in the camera to which the distancemeasuring apparatus according to the third aspect of the presentinvention is applied;

FIG. 30 is a flow chart showing a "Subject Distance Measuring Operation"subroutine for a camera to which a distance measuring apparatusaccording to the third or fourth aspect of the present invention isapplied;

FIG. 31 is a flow chart showing a "Macro AF Operation" subroutine for amacro AF operation in a camera to which a distance measuring apparatusaccording to the third aspect of the present invention is applied;

FIGS. 32A, B, C, and D represent a schematic view showing lightreceiving areas for Spot AF, in a camera to which a distance measuringapparatus according to the fourth aspect of the present invention isapplied;

FIGS. 33 and 34 are flow charts showing a "Spot AF Operation" in acamera to which the distance measuring apparatus to which the fourthaspect of the present invention is applied;

FIG. 35 is a front elevational view of a camera having a distancemeasuring apparatus according to a fifth, sixth, seventh or eighthaspect of the present invention;

FIG. 36 is a back view of the camera shown in FIG. 35;

FIG. 37 is a block diagram of the main components of a circuit of thecamera shown in FIG. 35;

FIG. 38 is a schematic view of an internal structure of a distancemeasuring unit in the camera shown in FIG. 35;

FIG. 39 is an explanatory view of the principle of a measurement by thedistance measuring unit, according to the fifth, sixth or seventh aspectof the invention;

FIG. 40 is a schematic view showing a relationship between lightreceiving areas used for a multiple measurement and the line sensors inthe camera shown in FIG. 35;

FIG. 41 is a schematic view of light receiving areas of a line sensor inthe camera shown in FIG. 35;

FIG. 42 is a diagram showing a location of photodiodes which are used inan evaluation function operation f(N) in the camera to which a distancemeasuring apparatus according to the fifth, sixth or seventh aspect ofthe present invention is applied:

FIGS. 43(A), 43(B) and 43(C) show graphs of image data detected by thedistance measuring unit, image data of light receiving areas, andevaluation values thereof in a camera to which a distance measuringapparatus according to the fifth or eighth aspect of the presentinvention is applied;

FIGS. 44(A), 44(B) and 44(C) show graphs of conventional image data,image data of light receiving areas, and evaluation values thereof whenthe amounts of light received by a pair of line sensors of a distancemeasuring unit are not balanced;

FIGS. 45A, B, and C show graphs of image data, image data of lightreceiving areas, and evaluation values thereof when the amount of lightreceived by one line sensor of a distance measuring unit is imbalancedwith that received by the other line sensor in a camera to which adistance measuring apparatus according to the fifth aspect of thepresent invention is applied;

FIG. 46 is a flow chart of the main operations of a camera to which adistance measuring apparatus according to the fifth, sixth, seventh oreighth aspect Of the present invention is applied;

FIGS. 47 and 48 are flow charts showing a "Photographing Operation"subroutine in the main operation shown in FIG. 46;

FIGS. 49 and 50 are flow charts showing a "Subject Distance MeasuringOperation" subroutine in the photographing operation shown in FIGS. 47and 48;

FIG. 51 is a flow chart showing a "Measuring Area Setting Operation"subroutine in the subroutine shown in FIGS. 49 and 50, in a camera towhich a distance measuring apparatus according to the fifth, sixth orseventh aspect of the present invention is applied;

FIG. 52 is a flow chart showing a "Data Correcting Operation" subroutinein the subroutine shown in FIGS. 49 and 50;

FIGS. 53 and 54 are flow charts showing a "Sensor Correcting Operation"in the subroutine shown in FIG. 52;

FIG. 55 is a flow chart showing an "Interpolation Arithmetic Operation"subroutine in a camera to which a distance measuring apparatus accordingto the fifth aspect of the present invention is applied;

FIG. 56 is a flow chart showing an "Evaluation Function f(N)" subroutinefor an operation to calculate an evaluation function f(N) in a camera towhich a distance measuring apparatus according to the fifth, sixth orseventh aspect of the present invention is applied;

FIG. 57 is an explanatory view to obtain a minimum value of theevaluation function f(N) by interpolation;

FIGS. 58(a), 58(b), 58(c), 58(A), 58(B) and 58(C) show graphs of imagedata and evaluation data thereof according to the prior art, and imagedata and evaluation values thereof according to the present invention,in a camera to which a distance measuring apparatus according to thesixth aspect of the present invention is applied, when the lightreceiving areas of the left and right line sensors in the distancemeasuring unit are at a low contrast;

FIGS. 59(a), 59(b), 59(c), 59(A), 59(B) and 59(C) show graphs of imagedata and evaluation data thereof according to the prior art, and imagedata and evaluation values thereof according to the present invention,in a camera to which a distance measuring apparatus according to thesixth aspect of the present invention is applied, when there are imagesof subjects at close distance and far distance in the same lightreceiving area of the left and right line sensors in the distancemeasuring unit;

FIG. 60 is a flow chart showing a "Subject Distance Measuring Operation"subroutine in a camera to which a distance measuring apparatus accordingto the sixth aspect of the present invention is applied;

FIG. 61 is a flow chart showing an "Interpolation Arithmetic Operation"subroutine in a camera to which a distance measuring apparatus accordingto the sixth or seventh aspect of the present invention is applied;

FIG. 62 is a flow chart showing a "Default Check Operation" subroutinein a camera to which a distance measuring apparatus according to thesixth or seventh aspect of the present invention is applied;

FIG. 63 is a flow chart showing a "Measuring Area Resetting Operation"subroutine in a camera to which a distance measuring apparatus accordingto the sixth aspect of the present invention is applied;

FIG. 64 is a flow chart showing a "Subject Image Distance ValueCalculating and Selecting Operation" subroutine in a camera to which adistance measuring apparatus according to the seventh aspect of thepresent invention is applied;

FIG. 65 is a flow chart showing a "Maximum Value Selecting Operation"subroutine in a camera to which a distance measuring apparatus accordingto the seventh aspect of the present invention is applied:

FIG. 66 shows a relationship between the light receiving areas used fora multiple measurement and line sensors, in a camera to which a distancemeasuring apparatus according to an eighth aspect of the presentinvention is applied;

FIG. 67 is a diagram showing a relationship between light receivingareas of a line sensor in the camera shown in FIG. 66;

FIG. 68 is a flow chart of a "Subject Distance Measuring Operation"subroutine in the camera to which a distance measuring apparatusaccording to the eighth aspect of the present invention is applied;

FIG. 69 is a flow chart showing a "Passive AF Unit Reset Operation"subroutine in the camera to which a distance measuring apparatusaccording to the eighth aspect of the present invention is applied;

FIG. 70 is a flow chart showing a "Sub-Photometering Operation"subroutine in the camera to which a distance measuring apparatusaccording to the eighth aspect of the present invention is applied; and,

FIG. 71 is a flow chart showing an "AE Calculating Operation" subroutinefor an AE calculating operation in the camera to which a distancemeasuring according to the eighth aspect is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment (i.e., a first embodiment) of a camera to which a distancemeasuring apparatus according to a first aspect of the present inventionis applied, will be discussed below with reference to FIGS. 1 through17. In the illustrated embodiment, a camera 11 is a lens-shutter typecamera provided with a distance measuring unit 18. In the camera 11, theoptical axis of the distance measurement optical system in the distancemeasuring unit 18 is not coincident with either the optical axis of thephotographing optical system or the optical axis of the finder opticalsystem.

The camera 11 is provided on its front, as shown in FIG. 1, with aphotographing lens (i.e., photographing optical system) 13 having anelectrically-driven zoom lens, a remote-control light receiving portion14, a light emitter 10 for indicating that a self-timer is in operation,a light receiving window 15, an AF auxiliary light emitter 16, a finderobjective window 17, a light receiving window 18' and a strobe emitter19. Behind the light receiving window 18' are placed a pair of imageforming lenses (i.e., distance measurement optical system) 25 and 26 ofthe distance measuring unit 18.

The camera 11 is provided on its back, as shown in FIG. 2, with a findereyepiece window 24, a main switch 65, a zooming lever 21 and an openableback cover 22. The zooming lever 21 can be moved in either a telephotodirection T, or a wide-angle direction W. When the zooming lever 21 ismoved towards a telephoto side or a wide-angle side, the photographinglens 13 is respectively moved in the telephoto direction or thewide-angle direction to perform the zooming operation.

The camera 11 is further provided on its upper side, as shown in FIG. 3,with a release button 20 and an external LCD 23 for indicating variousphotographic information. A strobe switch 40, a mode selecting switch41, a date switch 42, a spot AF selecting switch 43 and a drive switch45 are all provided around the external LCD 23. A macro switch 46 ispositioned at the rear of the release button 20. The date switch 42 isused for adjusting the date, altering the date indicating pattern in theexternal LCD 23 and altering the date exposure pattern on a film. Thedate altering mode can be selected by continuously depressing the dateswitch 42 for 3 seconds. By depressing the drive switch 45 the shutterdrive mode can be selectively changed to a single-frame mode, aconsecutive shooting mode, a self-timer shooting mode, and a bulb mode,etc.

The controlling system of the camera 11 will be explained below withreference to FIG. 4.

The camera 11 is provided with a CPU 50 for controlling various kinds ofphotographing operations. The CPU 50 starts controlling each operationin accordance with a predetermined program stored in an inner memory ofthe CPU 50.

A zoom motor driving circuit 53, a film motor driving circuit 54 and alight emitter driving circuit 55 are connected to the CPU 50. The zoommotor driving circuit 53 actuates a zoom motor 51 to drive thephotographing lens 13. The film motor driving circuit 54 actuates a filmmotor 52 for winding and rewinding a film. The light emitter drivingcircuit 55 actuates a red light emitter 12a, a green light emitter 12band the light emitter 10 to be in ON, OFF or blinked states. The red andgreen light emitters 12a and 12b are disposed at a position adjacent toa finder view 47 (shown in FIG. 10) in the finder so that red and greenlights emitted from the emitters 12a and 12b, respectively, can beobserved through the finder. The red light emitter 12a indicates whethera strobe light is now available or not, while the green light emitter12b indicates whether a subject is in focus or not.

The external LCD 23, a finder LCD 57, a strobe circuit 58 for actuatingthe strobe emitter 19, the distance measuring unit 18, the AF auxiliarylight emitter 16, a photometering circuit 62 and a temperature detectingcircuit 63 are connected to the CPU 50. The finder LCD 57 is placed inthe finder and is capable of indicating a plurality of focus frames Fa,Fb, Fc and Fd in the finder view 47. The photometering circuit 62calculates a photometric value in accordance with data detected by alight receiver, e.g., a CdS cell (cadmium sulfide cell), disposed behindthe light receiving window 15. The temperature detecting circuit 63detects the ambient temperature around the camera 11 in accordance withsignals outputted from a thermo-sensor, such as a thermistor.

A back cover switch 64, the main switch 65, a telephoto switch 66, awide-angle switch 67, a panorama switch 68, the strobe switch 40, themode selecting switch 41, the date switch 42, the spot AF selectingswitch 43, the drive switch 45, a photometering switch 74, a releaseswitch 75 and the macro switch 46 are connected to the CPU 50.

The mode selecting switch 41 is used to select a desired photographingmode from among a plurality of predetermined photographing modes. Thepredetermined photographing modes include a Multi-AF mode and a Spot AFmode. The mode selecting switch 41 can also select a strobe prohibitionmode. The photometering switch 74 is turned ON when the release button20 is half-depressed and the release switch 75 is turned ON when therelease button 20 is fully depressed.

A DX-code data reading circuit 77, a lens information reading circuit78, a date LED drive circuit 79, a film motion detecting circuit 81, anEEPROM 82, a RAM 83 and a ROM 84 are connected to the CPU 50. TheDX-code data reading circuit 77 reads ISO speed information printed on afilm patrone through DX-code contact pins (not shown). The lensinformation reading circuit 78 reads zoom information concerning thephotographing lens 13. The date LED drive circuit 79 actuates a7-segment digital display 80, to expose date or time information inaccordance with the operation of the date switch 42.

As shown in FIG. 5, the distance measuring unit 18 is provided with thepair of image forming lenses 25 and 26, and a pair of line sensors 27and 28. The pair of image forming lenses 25 and 26 are disposed suchthat they are apart from each other by a distance equal to the baselength. The subject images of a common subject are formed on each of thepair of line sensors 27 and 28 through the pair of image forming lenses25 and 26, respectively. The pair of line sensors 27 and 28 have thesame shape and each is provided with a plurality of light receivingelements (i.e., photodiodes) aligned in left and right directions of thecamera 11, so as to cover the maximum angle of view of the photographinglens 13.

A general method for measuring a subject distance through a pair of linesensors 27' and 28' based on triangulation will be explained below withreference to FIG. 6.

In FIG. 6, "f" presents the focal length of the image forming lenses 25'and 26'. "OA₁ " and "OA₂ " represent the optical axes of the imageforming lenses 25' and 26', respectively, which are disposed parallel toeach other and apart from each other by a distance "B". "b₁ " and "b₂ "represent the points of incidence of the optical axes OA₁ and OA₂ uponthe line sensors 27' and 28', respectively. Accordingly, the distancebetween the incident points b₁ and b₂ is the base length which is equalto the distance B. "P" represents a subject and "Lx" represents thedistance from the subject P to the pair of image forming lenses 25' and26'. Here, for the purpose of illustration, the subject P is regarded asa mere point having no length or width. It is assumed that images of thesubject P, located at the subject distance Lx, are respectively formedat the points X₁ and X₂ on the line sensors 27' and 28' by therespective image forming lenses 25' and 26', and that the distancebetween the image points X₁ and X₂ is "x". It is also assumed that thedistance between the points b1 and X₁ is XL, and the distance betweenthe points b2 and X₂ is XR. Accordingly, the following relation can beobtained:

    B:(XL+XR)=Lx:f

The subject distance Lx is given by:

    Lx=B×f/(XL+XR)=B×f/(x-B)

In the illustrated embodiment, the focal length f of the image forminglenses 25' and 26' and the distance therebetween, i.e., the base lengthB, are fixed values. Consequently, the subject distance Lx can beobtained by calculating the distances XL and XR or the distance x. Inthis embodiment, the image points X₁ and X₂ are detected to obtain thedistance x to thereby obtain the subject distance Lx.

In general, a subject to be photographed is not merely a point and hencethe subject images to be formed on the line sensors 27' and 28' are twodimensional. Therefore, the image points X₁ and X₂ cannot be directlydetected.

To solve this, a predetermined number of light receiving elements (e.g.1 or 2 elements) of the line sensor 27' are compared with the samenumber of light receiving elements of the line sensor 28'. Thiscomparison is repeatedly carried out while relatively changing the lightreceiving elements to be compared. When the highest degree ofcoincidence of the distribution of the quantity of light defined by thelight receiving elements between the line sensors 27' and 28' isobtained, the distance between the light receiving elements isdetermined to be the image distance x.

A plurality of light receiving areas are designated correspondingly oneach of the pair of line sensors 27 and 28. Each light receiving areaincludes a predetermined number of light receiving elements.

The CPU 50 shifts or varies the plurality of light receiving areas to beused on each of the line sensors 27, 28, in accordance with dataregarding focal length range information outputted from the RAM 83. Thisfocal length range information is stored in the RAM 83 when zooming iseffected in accordance with the information outputted from the lensinformation reading circuit 78. The four predetermined sets of positions(a), (b), (c) and (d) as shown in FIG. 9 are each stored in the ROM 84.

More specifically, each line sensor 27, 28 includes at least 128 lightreceiving elements aligned side by side. As shown in FIG. 8, each linesensor has five light receiving areas, namely, a center light receivingarea C (i.e., first light receiving area), a light receiving area LC(i.e., second light receiving area), a light receiving area RC (i.e.,third light receiving area), a left light receiving area L (i.e., fourthlight receiving area) and a right light receiving area R (i.e., fifthlight receiving area). Each of the five light receiving areas C, LC, RC,L and R include 36 light receiving elements. The light receiving area LCoverlaps the right portion of the left light receiving area L by 13light receiving elements and the left portion of the center lightreceiving area C by 13 light receiving elements. Likewise, the lightreceiving area RC overlaps the right portion of the center lightreceiving area C by 13 light receiving elements and the left portion ofthe right light receiving area R by 13 light receiving elements.

The reason why such a structure, in which two adjacent light receivingareas overlap each other by a predetermined amount, is adopted is thatdistance information cannot be obtained in a case where the contrasts ofa subject are formed only on the borders between light receiving areas,since the contrast is not detected at either light receiving area. Asshown in FIG. 7, the light receiving areas C, L, R, LC and RC correspondto subject light receivable ranges C', L', R', LC' and RC',respectively. In practice, each line sensor 27, 28 is comprised of morethan 128 light receiving elements so that each of the left and rightedges of the line sensor may have a margin.

The method for measuring a subject distance by selectively utilizing thelight receiving areas C, L, R, LC and RC of the pair of line sensors 27and 28 is hereinafter referred to as "Multi-AF".

The method for measuring a subject distance by selectively utilizing thelight receiving areas C, LC and RC of the pair of line sensors 27 and 28is hereinafter referred to as "Spot AF".

A plurality of images of a common subject are formed on each of the pairof line sensors 27 and 28 at different areas thereon through respectiveimage forming lenses 25 and 26. The amount of light, which is receivedby each line sensor 27, 28 and stored as electric charge therein, isconverted into electric signals, and these electric signals are sent tothe CPU 50 through a corresponding quantizing portion 29, 30 and anarithmetic operating portion 31 disposed in the distance measurementunit 18.

More specifically, a comparator and a latch circuit, included in thecorresponding quantizing portion 29 or 30, are connected to each lightreceiving element, and the electric charge accumulated in each lightreceiving element is quantized through the corresponding comparator andlatch circuit. The quantized data of each line sensor 27, 28 is sent tothe CPU 50 in serial order through the arithmetic operating portion 31.Amongst all the sensor data obtained from all of the light receivingelements on each line sensor 27, 28, the CPU 50 can only select a partof all the sensor data correspondingly from each line sensor 27, 28 anduse only this selected sensor data for a distance measuring operation.

When the Multi-AF mode is selected by the mode selecting switch 41, theCPU 50 selects one of the four patterns of positions (a), (b), (c) or(d) (FIG. 9) corresponding to the focal length range information of thephotographing lens 13 stored in the RAM 83, in accordance with theposition data of the light receiving areas read from the ROM 84.Thereafter, the CPU 50 receives the small sets of signals (i.e.,distance information) of the selected pattern of positions (a), (b), (c)or (d) from the arithmetic operating portion 31 and calculates a subjectdistance according to the signals to thereby obtain a displacement ofthe focusing lens. The focusing lens is driven to a point correspondingto the displacement thus obtained, by an exposure/focus drive circuit59.

In the case when the Multi-AF mode is selected by the mode selectingswitch 41, the focal length variable range (i.e., zooming range) of thephotographing lens 13 is divided into four ranges, namely, first,second, third and fourth ranges, in respective order from the wide-angleextremity to the telephoto extremity. The control of the camera 11varies the positions of the light receiving areas L, R, LC and RCrelative to the position of the center light receiving area C in such amanner as shown in FIG. 9, in accordance with a variation of focallength due to the zooming operation. Namely, the CPU 50 selects one ofthe predetermined patterns of positions of light receiving areas on eachline sensor 27, 28, i.e., the patterns of positions (a), (b), (c) or(d), according to the data regarding focal length range informationstored in RAM 83, when a focal length is varied in the zoomingoperation. Although the positions of the light receiving areas L, R, LCand RC shift relative to the position of the center light receiving areaC when one pattern of positions (a), (b), (c) or (d) is changed toanother pattern, each light receiving area is always comprised of 36light receiving elements.

As shown in FIG. 10, the finder LCD 57 of the camera 11 is provided withfour AF frames Fa, Fb, Fc and Fd, each of different sizes, whichrespectively correspond to the patterns of positions (a), (b), (c) and(d) shown in FIG. 9. The four AF frames can be seen in the finder view47. Each AF frame (i.e., measurement zone) consists of a pair of leftand right parenthesis-like LCD segments. Only the AF frame Fa isactivated, i.e., becomes visible, when the pattern of positions (a) isselected, and the photographing lens 13 is at the wide-angle extremity.Likewise, only the AF frame Fd is activated, i.e., becomes visible, whenthe pattern of positions (d) is selected, and the photographing lens 13is at the telephoto extremity. When zooming is effected from thewide-angle extremity to the telephoto extremity, the effective patternof positions changes from (a) to (d) and the activated AF frame shiftsfrom Fa to Fd. Accordingly, in the camera 11, the AF frame ormeasurement zone is wide at the telephoto side and is narrow at thewide-angle side in accordance with a variation in the focal length ofthe photographing lens 13. With this structure, the large difference insize between the actual light receiving range and the AF frame is almostcompletely reduced, and the photographer can thus visually confirm theactual size of the light receiving range at a current selected focallength.

The operation of the camera 11 having the above mentioned circuitstructure will be hereinafter discussed in reference to the flow chartsshown in FIGS. 11 to 17. The operation of the camera 11 is carried outby the CPU 50 in accordance with predetermined programs stored in theROM 84.

When the main switch 65 is turned ON to supply electricity to eachcircuit, the control enters into the main routine shown in FIG. 11. Inthis main routine, switch information, such as ON/OFF state information,is inputted to the main CPU 50 from each of all the switches connectedto the CPU 50, such as the photometering switch 74, at Step S1.Thereafter, the ON/OFF state of the back cover switch 64 is checked atStep S2. If it is determined that the back cover switch 64 is OFF, it isjudged that the back cover 22 is closed and the control proceeds to StepS3. Conversely, if it is checked that the back cover switch 64 is ON, itis judged that the back cover 22 is open and the control proceeds toStep S4. At Step S4 it is checked whether or not a film loadingoperation has completed. The control proceeds to Step S3 if it ischecked that the film loading operation has been completed. If not, thecontrol proceeds to a subroutine labeled "Loading Operation" at Step S5to carry out the film loading operation.

At Step S3, it is checked whether or not the photographing lens 13 ispositioned at its lens retracted position in accordance with the zoominformation read from the lens information reading circuit 78. Thecontrol proceeds to Step S7 where it is checked if that thephotographing lens 13 is placed at its lens retracted position, or ifnot proceeds to Step S6. At Step S7, it is checked if the main switch 65is turned ON from its OFF state, and if it is turned ON the controlproceeds to a subroutine labeled "Lens Advancing Operation" at Step S8,in which the photographing lens 13 is advanced by a small amount fromits retracted position to an initial position corresponding to thewide-angle extremity. If the main switch 65 is not turned ON at Step S7,the control proceeds to a subroutine labeled "Power Down Operation" atStep S9.

At Step S6 it is checked if the main switch 65 is turned ON from its OFFstate. If the main switch 65 is turned ON, it is judged that the camera11 has just been activated and the control proceeds to Step S11 tointerrupt the date altering mode, if the date altering mode is inoperation, and to display the newly inputted date on the external LCD23. At Step S11, if the date altering mode is not in operation, the datewhich was previously set is displayed on the external LCD 23.Thereafter, the control proceeds to a subroutine labeled "LensRetraction Operation" at Step S12. At Step S6 if it is judged that themain switch 65 is not turned ON from its OFF state, the control proceedsto Step S10 to check the state of the telephoto switch 66, i.e., turnedON or OFF. If it is checked that the telephoto switch 66 is turned ON atStep S10, it is then checked whether or not the date altering mode is inoperation at Step S14. If it is determined that the telephoto switch 66is not operated at Step S10, the control proceeds to Step S13.

If it is determined that the date altering mode is not in operation atStep S14, the control proceeds to Step S15 to check if the photographinglens 13 is positioned at its telephoto extremity. If it is determinedthat the date altering mode is in operation at Step S14, the controlproceeds to a subroutine labeled "Adding Adjustment Operation" at StepS16. The subroutine "Adding Adjustment Operation" is provided to adjustthe date or time displayed on the external LCD 23 in the date alteringmode, by increasing the day, month, year, hour or minute which isselected to be adjusted through a subroutine labeled "Adjusting PositionShifting Operation" at Step S52 (FIG. 13).

At Step S15 if it is determined that the photographing lens 13 ispositioned at its telephoto extremity, the control proceeds to Step S13to check if the wide-angle switch 67 is operated, i.e., turned ON orOFF. Conversely, if at Step S15 the photographing lens 13 is notpositioned at its telephoto extremity, the control proceeds to Step S17to check whether or not the photographing lens 13 is positioned at itsmacro position, in accordance with the zoom information read out fromthe lens information reading circuit 78.

If it is determined that the photographing lens 13 is positioned at itsmacro position at Step S17, the control proceeds to a subroutine labeled"Driving to Telephoto Extremity Operation" at Step S19 to move thephotographing lens 13 from the macro position to the telephotoextremity. Conversely, if the photographing lens 13 is not positioned atits macro position at Step S17, the control proceeds to a subroutinelabeled "Zooming toward Telephoto Extremity Operation" at Step S18 tomove the photographing lens 13 from its current position towards thetelephoto extremity.

At Step S13, if it is determined that the wide-angle switch 67 is turnedON, the control proceeds to Step S20 to check if the date altering modeis in operation, or to Step S26 if it is determined that the wide-angleswitch 67 is turned OFF.

If it is determined that the date altering mode is in operation at StepS20, the control proceeds to a subroutine labeled "SubtractingAdjustment Operation" at Step S22. If the date altering mode is not inoperation, it is then checked whether the photographing lens 13 ispositioned at its wide-angle extremity at Step S21. The subroutine"Subtracting Adjustment Operation" at Step S22 is to adjust the date ortime displayed on the external LCD 23 in the date altering mode, bydecreasing the number of day, month, year, hour or minute which isselected to be adjusted through the subroutine "Adjusting PositionShifting Operation" at Step S52.

At Step S21 if the photographing lens 13 is positioned at its wide-angleextremity, the control then proceeds to Step S26, or to Step S23 if not.

At Step S23 it is checked if the photographing lens 13 is positioned atits macro position. If the photographing lens 13 is positioned at itsmacro position the control proceeds to a subroutine labeled "Driving toTelephoto Extremity Operation" at Step S25 to move the photographinglens 13 from the macro position to the telephoto extremity. If thephotographing lens 13 is not at its macro position at Step S23, thecontrol proceeds to a subroutine labeled "Zooming toward Wide-AngleExtremity Operation" at Step S24, to move the photographing lens 13 fromits current position towards the wide-angle extremity.

At Step S26 (FIG. 12) it is checked whether or not the macro switch 46is turned ON. If it is determined that the macro switch 46 is turned ON,the control proceeds to Step S28 to check if the photographing lens 13is positioned at its macro position, or to Step S27 if it is determinedthat the macro switch 46 is turned OFF.

At Step S28 if it is determined that the photographing lens 13 ispositioned at its macro position, the control proceeds to Step S27.Conversely, if the photographing lens 13 is not positioned at its macroposition control proceeds to a subroutine labeled "Driving to MacroPosition Operation" at Step S29, to move the photographing lens 13 toits macro position.

At Step S27 it is determined if the drive switch 45 is turned ON fromits OFF state, and the control proceeds to Step S31 if turned ON, or toStep S30 if not.

At Step S31 if it is determined that the date altering mode is inoperation control returns to Step S1. If the date altering mode is notin operation control proceeds to a subroutine labeled "Shutter DriveSetting Operation" at Step S32.

After completing the subroutine "Shutter Drive Setting Operation", thecontrol proceeds to Step S33 to check if the drive switch 45 is turnedON or OFF. The control returns to Step S1 if the drive switch 45 isturned OFF. If it is determined that the drive switch 45 is turned ON, atimer provided in the CPU 50 starts and the control proceeds to StepS34. The timer continues to count while the drive switch 45 isdepressed, i.e., keeps its ON state, but is reset if the drive switch 45is turned OFF.

At Step S34, it is checked if three seconds has elapsed since the timerstarted. If three seconds has already elapsed, the control proceeds toStep S35 to check if the release switch 75 is turned ON. If threeseconds has not yet elapsed, the control goes back to Step S33.

At Step S35, if it is determined that the release switch 75 is turnedON, the control proceeds to a subroutine labeled "Drive Lens toWide-Angle Extremity Operation" at Step S36, and thereafter, furtherproceeds to a subroutine labeled "Rewind Operation" at Step S37 torewind the film. Thereafter, the control returns to Step S1. If it isdetermined that the release switch 75 is turned OFF at Step S35, controlreturns to Step S33.

At Step S30 it is checked whether the mode selecting switch 41 is turnedON from its OFF state, and the control proceeds to Step S38 if it isturned ON, or to Step S40 if not.

At Step S38 it is checked whether or not the date altering mode is inoperation, and the control returns to Step S1 if the date altering modeis in operation, or to a subroutine labeled "Mode Setting Operation" atStep S39, if the date altering mode is not in operation. In thesubroutine "Mode Setting Operation", the aforementioned Spot AF orMulti-AF can be set as the subject distance measuring mode. At Step S40(FIG. 13) it is checked if the strobe switch 40 is turned ON from itsOFF state. The control proceeds to Step S42 if turned ON, or to Step S41if not.

At Step S42 it is checked if the date altering mode is in operation. Thecontrol returns to Step S1 if the date altering mode is in operation, orto Step S43 if not in operation. At Step S43 it is checked if the strobeprohibition mode is selected by the mode selecting switch 41 and inoperation. The control proceeds to Step S44 if in operation, or returnsto Step S1 if not in operation.

At Step S44, if a red-eye reduction mode is turned ON, it is temporarilyturned OFF while the strobe prohibition mode is in operation. After thestrobe prohibition mode has been cancelled, the red-eye reduction modereturns.

At Step S41, it is checked if the date switch 42 is turned ON from itsOFF state, and the control proceeds to Step S46 if turned ON, or to StepS45 if not.

In the date altering mode, when the external LCD 23 indicates the date,for example, "95 2 3" (i.e., 1995, Feb. 3rd), when one of the numeralsblinks, i.e., "95", "2" or "3", this indicates that the number blinkingis presently adjustable. The blinking number can be increased ordecreased by respectively operating the zooming switch 21 in thetelephoto direction T (i.e., in the right hand direction) or thewide-angle direction W (i.e., in the left hand direction). With eachdepression of the date switch 42 (or when it is turned ON), the numbercurrently blinking changes to the next number on the right, in the order"95", "2", "3", "95", "2", "3", etc.

At Step S46 it is checked if the date altering mode is in operation, andif in operation, the control then proceeds to a subroutine labeled"Adjusting Position Shifting Operation" at Step S52, at which the numbercurrently blinking in the external LCD 23 changes or shifts to the nextnumber on the right. The control returns to Step S1 after the completionof Step S52.

If the date altering mode is not in operation at Step S46, the controlproceeds to Step S47 to change the previously selected form of dateindication, displayed on the external LCD 23, to another form of dateindication. Here, it should be noted that there are various forms forindicating the date. For instance, supposing that the date is Feb. 3,1996, and that the time is nine o'clock and twenty five minutes (am).This information can be indicated on the external LCD 23 in any of thefollowing five forms: 1st Form "2 3 96" (i.e., month, day, year); 2ndForm "3 2 96" (i.e., day, month, year); 3rd Form "96 2 3" (i.e., year,month, day); 4th Form "3 09:25" (i.e., day, hour, minute); or, 5th Form". . . " (i.e., no date information is exposed on the film).Accordingly, when the date altering mode is not operated, the previouslyselected date indication form is changed to another indication form eachtime the date switch 42 is depressed.

After Step S47 the control proceeds to a subroutine labeled "DateDisplay Operation" at Step S48 to indicate the current date informationin the selected indication form.

When Step S47 has completed, the control proceeds to Step S49 to checkthe ON/OFF state of the date switch 42 The control returns to Step S1 ifthe date switch 42 is turned OFF If the date switch 42 is turned ON, atimer provided in the CPU 50 starts and the control proceeds to StepS50. The timer continues to count while the date switch 42 is depressed,i.e., keeps its ON state, and is reset when the date switch 42 is turnedOFF.

At Step S50, it is checked if three seconds has elapsed since the timerstarted. If three seconds has already elapsed, the control proceeds toStep S51 to enter the date altering mode, in which any one of theabove-mentioned date indication forms could be indicated on the externalLCD 23, e.g., the 3rd Form "96 2 3". Since three seconds has elapsed thefirst numeral on the left of the date indicated, i.e. "96", startsblinking, thereafter, the control returns to Step S1. If three secondshas not yet elapsed, the control returns to Step S49.

At Step S45 it is checked if the photometering switch 74 is turned ONfrom its OFF state, and the control proceeds to Step S54 if it is turnedON, or to Step S53 if not.

At Step S54 it is checked if a film loading error is detected, and thecontrol proceeds to Step S53 if it is detected, or if no error isdetected to Step S55 to check if the film rewinding has completed. Thecontrol proceeds to Step S53 if it is judged that the film rewinding hasalready completed at Step S55, or to a subroutine labelled"Photographing Operation" at Step S56 (FIGS. 14 and 15), if the filmrewinding has not completed. After completing the subroutine"Photographing Operation", the control proceeds to Step S53.

At Step S53 it is checked whether or not there is a strobe chargerequirement, and the control proceeds to a subroutine labelled "StrobeCharge Operation" at Step S58 if a strobe charge is required, or to asubroutine labelled "Power Down Operation" at Step S57 if strobecharging is not required.

FIGS. 14 and 15 show the subroutine "Photographing Operation" at StepS56. In this subroutine, firstly, the ISO film speed printed on theloaded film patrone is read through the DX-code data reading circuit 77at Step S60. Thereafter, the remaining capacity of the battery ischecked at Step S61. At Step S62 it is checked if there is any errordetected at Step S60 or Step S61, and the control returns if any erroris detected, or proceeds to a subroutine labelled "Multi-AF Operation"at Step S63 if there is no error. After the completion of Step S63 apredetermined photometering calculation is performed by thephotometering circuit 62 at Step S64, and subsequently, a predeterminedAE calculation is performed at Step S65.

At Step S67 it is checked whether or not the subject distance valueusable for photography has been calculated (i.e., it is checked if thereis any error in the subject distance calculation), and the controlproceeds to Step S71 if it is judged that the subject distance valueusable for photography has not been calculated (i.e., there is nosubject distance value calculated), or to Step S68 if it is judged thatthe subject distance value usable for photography has been calculated(i.e., there is a subject distance value calculated).

At Step S71 the green light emitter 12b is blinked so as to inform thephotographer that an in-focus state cannot be obtained. At Step S68 itis checked whether or not a subject to be photographed is located tooclose to the camera 11 to be in-focus, and the control proceeds to StepS71 if the subject is too close, or to Step S69 if not. At Step S69 thegreen light emitter 12b is lit to inform the photographer that thesubject to be photographed is now in focus.

At Step S70 it is checked if there is a strobe light emittingrequirement, and the control proceeds to Step S72 if there is arequirement, or to Step S76 if no requirement exists. At Step S72 an FM(Flashmatic) calculation is performed, and subsequently, it is checkedif the strobe condenser is fully charged at Step S73. The controlproceeds to Step S75 if the strobe condenser is fully charged, or toStep S74 if not fully charged. At Step S75 the red light emitter 12a islit to inform the photographer that the strobe is ready to fire. At StepS74 the red light emitter 12a is blinked to inform the photographer thatthe strobe is not yet ready to fire.

Step S76 is a subroutine labelled "Input Switch Information Operation",where the CPU 50 inputs switch information regarding each switch. AfterStep S76 the control proceeds to Step S77 to check the ON/OFF state ofthe release switch 75, and subsequently, the control proceeds to StepS78 if the release switch is turned ON, or to Step S79 if it is turnedOFF.

At Step S79 the ON/OFF state of the photometering switch 74 is checked,and the control returns to Step S76 if the photometering switch 74 isturned ON, or proceeds to Step S80 if it is turned OFF. At Step S80 thered light emitter 12a or the green light emitter 12b, which is eitherlit or is blinking, is turned OFF.

At Step S78 it is checked if a self-timer mode has been set by the driveswitch 45, and the control proceeds to a subroutine labelled "Self WaitOperation" at Step S81 if the self-timer mode has been set, or thecontrol returns if it is not set. The subroutine "Self Wait Operation"is to release a shutter when a predetermined time (e.g., seven seconds)has elapsed since the release button 20 has been fully depressed. AfterStep S81 the control proceeds to Step S82 to check if the self-timermode is interrupted while being in operation, and the control returns ifit has been interrupted, or proceeds to Step S83 if not.

At Step S83 (FIG. 15) the light emitter 10 is lit and the green lightemitter 12b and/or red light emitter 12a are turned OFF. Thereafter, thefocusing lens of the photographing lens 13 is driven for focusing atStep S84, and subsequently, the light emitter 10 is turned OFF at StepS85. The shutter is then released at Step S86, and after completion, thefilm is wound forward by one picture frame at Step S87.

After Step S87, it is checked at Step S88 if the auto rewind mode hasbeen set, and the control proceeds to Step S89 to rewind the film if theauto rewind mode has been set, or the control returns if it has not beenset The auto rewind mode can be selectively set or reset by pressing anauto rewind mode setting button (not shown) provided on the camera body.In the auto rewind mode, the film rewinding operation starts immediatelyafter the last picture frame of the film has been exposed.

FIGS. 16 and 17 show the subroutine "Multi-AF Operation" which is calledat Step S63 in FIG. 14.

Four sensor start numbers, ire., DIV 0, DIV 1, DIV 2 and DIV 3, whichrespectively correspond to the first, second, third and fourth ranges ofthe zooming range of the photographing lens 13, each determine theposition of each of the light receiving areas C, L, R, LC and RC, andare stored in the RAM 83 in accordance with the information read outfrom the lens information reading circuit 78 when the zooming operationor the macro operation is performed in accordance with the operation atStep S10, S13 or S26.

In the subroutine "Multi-AF Operation" at Step S63, under the conditionthat one effective set of the light receiving areas C, L, R, LC and RChaving one of the four predetermined sets of positions (a), (b), (c) and(d) (FIG. 9), has been already selected or determined in accordance withthe data of the above mentioned four sensor start numbers and the fourpredetermined sets of positions (a), (b), (c) and (d) stored in the ROM84, it is checked whether or not there is a default (i.e., the state inwhich a subject distance value cannot be measured) at any of the lightreceiving areas C, L, R, LC and RC, and among the subject distancevalues obtained with the light receiving areas each having no default,one subject distance value which is within a predetermined focus-capabledistance range and closest to the camera 11 is selected to be used forfocusing.

In the subroutine "Multi-AF Operation" at Step S63, firstly, the sensorstart number currently stored in the RAM 83 is read out from the RAM 83and it is checked if the read sensor start number is "DIV 0" or not atStep S90. The control proceeds to Step S102 if it is judged that theread sensor start number is "DIV 0". At Step S102, the CPU 50 inputs,from the ROM 84, the information regarding the read sensor start number"DIV 0", i.e., "C₋₋ DIV 0", "L₋₋ DIV 0", "R DIV 0", "LC₋₋ DIV 0" and"RC₋₋ DIV 0", whose respective positions are shown in FIG. 9(a).

Each positional information "C₋₋ DIV 0", "L₋₋ DIV 0", "R DIV 0", "LC₋₋DIV 0" and "RC₋₋ DIV 0" represents the position of the light receivingelement positioned at one end (the right end in FIG. 9) of thecorresponding light receiving area, which consists of 36 light receivingelements.

At Step S103, the effective positions of the light receiving areas C, L,R, LC and RC are each determined in accordance with the above mentionedinformation "C₋₋ DIV 0", "L₋₋ DIV 0", "R₋₋ DIV 0", "LC₋₋ DIV 0" and"RC₋₋ DIV 0", respectively, in the following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position "C₋₋ DIV 0", to the leftend. The position of the left end is determined by the amount "C₋₋ DIV0"+(N-1), i.e., "1+(N-1)". Here, "N " represents the predeterminednumber of light receiving elements of which each of the light receivingareas C, L, R, LC and RC consists, i.e., 36 in this embodiment. Thecenter light receiving area C can be expressed in the range defined by"C₋₋ DIV 0"˜"C₋₋ DIV 0"+(N-1). The rest of the light receiving areas L,R, LC and RC are each determined in a similar manner.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 0", to the leftend thereof by the amount "L₋₋ DIV 0"+(N-1), i.e., "1+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 0", to the leftend thereof by the amount "R₋₋ DIV 0"+(N-1), i.e., "1+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 0", to the left endthereof by the amount "LC₋₋ DIV 0"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 0", to the left endthereof by the amount "RC₋₋ DIV 0"+(N-1), i.e., "1+(N-1)".

The arithmetic operating portion 31 provided in the distance measurementunit 18 sends to the CPU 50, in sequence, the sensor data that isoutputted from each of the light receiving elements located on each ofthe light receiving areas C, L, R, LC and RC, in accordance with thesignals outputted from the main CPU 50. For instance, in the case whenit is necessary for the main CPU 50 to receive a series of sensor datafrom the right light receiving area R ranging from the 9th lightreceiving element (counted from the right end of the total 128 lightreceiving elements) to the left end of the right light receiving area R,the arithmetic operating portion 31 sends in sequence the sensor dataoutputted from each of the 36 light receiving elements ranging from theabove mentioned 9th light receiving element to the 44th light receivingelement (i.e., 9+(36-1)).

After Step S103, the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S96 in which it is checked whether there isa default at each of the light receiving areas C, L, R, LC and RC inaccordance with the inputted sensor data.

At Step S90, if it is judged that the read sensor start number is not"DIV 0", the control proceeds to Step S91 to check if the read sensorstart number is "DIV 1". If it is judged that the read sensor startnumber is "DIV 1", the control proceeds to Step S104. At Step S104, theCPU 50 inputs from the ROM 84, the positional information regarding theread sensor start number "DIV 1", i.e., "C DIV 1", "L₋₋ DIV 1", "R₋₋ DIV1", "LC₋₋ DIV 1" and "RC₋₋ DIV 1", whose respective positions are shownin FIG. 9(b).

Thereafter, at Step S105, the effective positions of the light receivingareas C, L, R, LC and RC are each determined in accordance with theabove mentioned information "C₋₋ DIV 1", "L₋₋ DIV 1", "R₋₋ DIV 1", "LC₋₋DIV 1" and "RC₋₋ DIV 1", respectively, in the following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position of "C₋₋ DIV 1", to the leftend. The position of the left end is determined by the amount "C₋₋ DIV1"+(N-1), i.e., "1+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 1"˜"C₋₋ DIV 1"+(N-1). Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 1", to the leftend thereof by the amount "L₋₋ DIV 1"+(N-1), i.e., "1+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 1", to the leftend thereof by the amount "R₋₋ DIV 1"+(N-1), i.e., "1+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 1", to the left endthereof by the amount "LC₋₋ DIV 1"+(N-1), i.e., "1+(N-1)".

The light receiving area PC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 1", to the left endthereof by the amount "RC₋₋ DIV 1"+(N-1), i.e., "1+(N-1)".

After Step S105 the control proceeds to the subroutine "DefaultDetecting Operation" at Step S96.

At Step S91, if it is judged that the read sensor start number is not"DIV 1", the control proceeds to Step S93 to check if the read sensorstart number is "DIV 2". If it is judged that the read sensor startnumber is "DIV 2", the control proceeds to Step S106. At Step S106, theCPU 50 inputs, from the ROM 84, the positional information regarding theread sensor start number "DIV 2", i.e., "C DIV 2", "L₋₋ DIV 2", "R₋₋ DIV2", "LC₋₋ DIV 2" and "RC₋₋ DIV 2", whose respective positions are shownin FIG. 9(c).

Thereafter, at Step S107, the effective positions of the light receivingareas C, L, R, LC and RC are each determined in accordance with theabove mentioned information "C₋₋ DIV 2", "L₋₋ DIV 2", "R₋₋ DIV 2", "LC₋₋DIV 2" and "RC₋₋ DIV 2", respectively, in the following manner.

That is, the center light receiving area C is determined by the widthfrom the right end, i.e., the position of "C₋₋ DIV 2", to the left end.The position of the left end is determined by the amount "C₋₋ DIV2"+(N-1), i.e., "1+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 2"˜"C₋₋ DIV 2"+(N-1). Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner, as follows.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 2", to the leftend thereof by the amount "L₋₋ DIV 2"+(N-1), i.e., "1+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 2", to the leftend thereof by the amount "R₋₋ DIV 2"+(N-1), i.e., "1+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 2", to the left endthereof by the amount "LC₋₋ DIV 2"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 2", to the left endthereof by the amount "RC₋₋ DIV 2"+(N-1), i.e., "1+(N-1)".

After Step S107 the control proceeds to the subroutine "DefaultDetecting Operation" at Step S96.

At Step S93, if it is judged that the read sensor start number is not"DIV 2", the control proceeds to Step S94. At Step S94, the CPU 50inputs, from the ROM 84, the positional information regarding the readsensor start number "DIV 3", i.e., "C₋₋ DIV 3", "L₋₋ DIV 3", "R₋₋ DIV3", "LC DIV 3" and "RC₋₋ DIV 3", whose respective positions are shown inFIG. 9(d).

Thereafter, at Step S95, the effective positions of the light receivingareas C, L, R, LC and RC are each determined in accordance with theabove mentioned information "C₋₋ DIV 3", "L₋₋ DIV 3", "R₋₋ DIV 3", "LC₋₋DIV 3" and "RC₋₋ DIV 3", respectively, in the following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position of "C₋₋ DIV 3", to the leftend. The position of the left end is determined by the amount "C₋₋ DIV3"+(N-1), i.e., "1+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 3"˜"C₋₋ DIV 3"+(N-1). Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner as follows.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 3", to the leftend thereof by the amount "L₋₋ DIV 3"+(N-1), i.e., "1+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 3", to the leftend thereof by the amount "R₋₋ DIV 3"+(N-1), i.e., "1+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 3", to the left endthereof by the amount "LC₋₋ DIV 3"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 3", to the left endthereof by the amount "RC₋₋ DIV 3"+(N-1), i.e., "1+(N-1)".

After Step S95 the control proceeds to the subroutine "Default DetectingOperation" at Step 596.

It should be noted here, shown in FIG. 9, as the photographing lens ismoved from the wide-angle extremity to the telephoto extremity, and theposition of light receiving area C does not change at all. However, thepositions of the light receiving areas L, LC, RC and R gradually shifttoward a more central position, i.e., the number of overlapped lightreceiving elements increases. Note, however, that each light receivingarea always consists of 36 light receiving elements.

In the subroutine "Default Detecting Operation" at Step S96, it ischecked whether there is a default at each of the light receiving areasC, L, R, LC and RC, determined in accordance with the inputted sensordata, i.e., in accordance with the selected focal length of thephotographing lens 13. In accordance with the result of this checking, aflag is set to correspond to each of the determined light receivingareas having no default. For instance, in the case where the lightreceiving areas LC and RC each have a default detected while the lightreceiving areas C, L and R each have no default detected, flags arerespectively set corresponding to the light receiving areas C, L and R.

After Step S96 the control proceeds to a subroutine labelled "ArithmeticOperation" at Step S97. Here a subject distance value is calculated foreach of the light receiving areas C, L, R, LC and RC, based ontriangulation as explained above with reference to FIG. 6. Note that"subject distance value" is a value corresponding to the distance of"x-B" (i.e., the distance "x" minus the distance "B") shown in FIG. 6.The calculated subject distance values for each of the light receivingareas C, L, R, LC and RC are respectively CX, LX, RX, LCX and RCX. Thelarger the subject distance value CX, LX, RX, LCX or RCX is, the closerthe corresponding subject to be photographed is located to the camera11.

After Step S97 the control proceeds to Step S98. At Step S98, thereference subject distance value "X" is set "0" (zero) as an initialvalue.

Thereafter, at Step S99 it is checked if there is a default at the lightreceiving area C. Here it is checked whether a flag is set to correspondto the light receiving area C. The control proceeds to Step S100 ifthere is no default at the light receiving area C, or to Step S108 ifthere is a default at the light receiving area C.

At Step S100, it is checked if the subject distance value CX is largerthan the reference subject distance value "X", and the control proceedsto Step S108 if the subject distance value CX is equal to or less thanthe reference subject distance value "X", or to Step S101 if the subjectdistance value CX is greater than the reference subject distance value"X". At Step S101, the reference subject distance value "X" is replacedby the subject distance value CX.

From Step S108 to S119, similar operations to those of Steps S99, S100and S101 are performed for each of the remaining light receiving areasL, R, LC and RC.

That is, at Step S108 it is checked if there is a default at the lightreceiving area LC by checking if there is a flag set corresponding tothe light receiving area LC, and the control proceeds to Step S109 ifthere is no default at the light receiving area LC, or to Step S111 ifthere is a default at the light receiving area LC.

At Step S109, it is checked if the subject distance value LCX is greaterthan the reference subject distance value "X", and the control proceedsto Step S111 if the subject distance value LCX is equal to or less thanthe reference subject distance value "X", or to Step S110 if the subjectdistance value LCX is greater than the reference subject distance value"X". At Step S110, the reference subject distance value "X" is replacedby the subject distance value LCX.

At Step S111 it is checked if there is a default at the light receivingarea RC. Here it is checked whether a flag is set to correspond to thelight receiving area RC, and the control proceeds to Step S112 if thereis no default at the light receiving area RC, or to Step S114 if thereis a default at the light receiving area RC.

At Step S112, it is checked if the subject distance value RCX is greaterthan the reference subject distance value "X", and the control proceedsto Step S114 if the subject distance value LCX is equal to or less thanthe reference subject distance value "X", or to Step S113 if the subjectdistance value RCX is greater than the reference subject distance value"X". At Step S113, the reference subject distance value "X" is replacedby the subject distance value RCX.

At Step S114 it is checked if there is a default at the light receivingarea L by checking if a flag is set to correspond to the light receivingarea L, and the control proceeds to Step S115 if there is no default atthe light receiving area L, or to Step S117 if there is a default at thelight receiving area L.

At Step S115, it is checked if the subject distance value LX is greaterthan the reference subject distance value "X", and the control proceedsto Step S117 if the subject distance value LX is equal to or less thanthe reference subject distance value "X", or to Step S116 if the subjectdistance value LX is greater than the reference subject distance value"X". At Step S116, the reference subject distance value "X" is replacedby the subject distance value LX.

At Step S117 it is determined if there is a default at the lightreceiving area R by checking if a flag is set corresponding to the lightreceiving area R. The control proceeds to Step S118 if there is nodefault at the light receiving area R, or the control returns to thecalling routine if there is a default at the light receiving area R.

At Step S118, it is checked if the subject distance value RX is greaterthan the reference subject distance value "X", and the control returnsif the subject distance value RX is equal to or less than the referencesubject distance value "X", or to Step S119 if the subject distancevalue RX is greater than the reference subject distance value "X". AtStep S119, the reference subject distance value "X" is replaced by thesubject distance value RX.

According to the operations from Step S99 to Step S119, a certain valueis obtained as the reference subject distance value "X". At Step S67 itis checked whether this obtained value is greater than "0" (zero). Ifthe value is equal to or less than "0", it represents that a subjectdistance value usable for photography has not been calculated (i.e., anin-focus state cannot be obtained). In this case, the control proceedsto Step S71 to make the green light emitter 12b blink so as to informthe photographer that an in-focus state cannot be obtained.

Conversely at Step S67, when the obtained value is greater than "0", itrepresents that a subject distance value usable for photography has beencalculated (i.e., an in-focus state has been obtained). In this case,the control proceeds to Step S68 to check whether or not a subject to bephotographed is located too close to the camera 11 to be in-focus, andthe control proceeds to Step S71 to make the green light emitter 12bblink if the subject is too close. If the subject is located at adistance where an in-focus state can be achieved, control proceeds toStep S69 and the green light emitter 12b is lit.

As can be understood from the foregoing, in the first embodiment ofcamera 11 having a distance measuring apparatus to which the firstaspect of the present invention is applied, the actual light receivingarea on each of the line sensors 27 and 28 is varied or adjusted inaccordance with the variation in size of the AF frame in the finder view47. Thus, according to the first embodiment the subject or subjects seenwithin the AF frame Fa, Fb, Fc or Fd is precisely focused in a reliablemanner, and the chances of the distance of a subject, that aPhotographer does not intend to photograph, being mistakenly measured asthe distance of a main subject are greatly reduced.

In the above first embodiment, the photographing optical system of thecamera 11 is comprised of a zoom lens (i.e., the photographing lens 13).However, instead of a zoom lens, the camera 11 may be provided with alens whose focal length can be selected from one of severalpredetermined focal lengths, e.g., a focal length selected from 38 mm,50 mm or 70 mm. In this case, the number of predetermined sets ofpositions of the light receiving areas will correspond to the number ofpredetermined focal lengths (i.e., if there are three predeterminedfocal lengths, there will be three predetermined sets of positions), andthese predetermined sets of positions may be prestored in the ROM 84,and one of the predetermined sets of positions may be selected tocorrespond to the selected one of the focal lengths.

As can be seen from the foregoing, according to the camera having adistance measuring apparatus to which the first aspect of the presentinvention is applied, since the actual light receiving area on each ofthe pair of line sensors is varied or adjusted in accordance with thevariation in size of the AF frame seen in the finder view, a subject(s)seen within the AF frame is precisely and reliably focused, andfurthermore, the chances of the distance of a subject, that aphotographer does not intend to photograph, being mistakenly measured asthe distance of a main subject are greatly reduced.

Another embodiment (i.e., a second embodiment) of a camera to which adistance measuring apparatus according to a second aspect of the presentinvention is applied will be discussed below. The camera of the secondembodiment is similar to the camera of the first embodiment to which thefirst aspect of the present invention is applied, except in severalrespects. In the following discussion only that structure unique to thesecond embodiment will be discussed. The camera of the second embodimentwill be explained below with reference to FIGS. 1˜9, 11˜13, 15, and18˜25.

Although the finder LCD 57 of the camera 11 of the first embodiment iscapable of indicating only the AF frame Fa, Fb, Fc and Fd, as shown inFIG. 10, the finder LCD 57 of the camera 11 of the second embodiment iscapable of further indicating, inside the AF frame Fa, four additionalAF frames fa, fb, fc and fd (FIG. 18). As has already been mentionedbefore, the method for measuring a subject distance by selectivelyutilizing the light receiving areas C, LC and RC of the pair of linesensors 27 and 28 is referred to as "Spot AF". The AF frames fa, fb, fcand fd are effectively utilized when this "Spot AF" is carried out. Thiswill be explained below.

When the Multi-AF mode is in operation, the activated AF frame shiftsfrom Fa to Fd when the effective pattern of positions of the lightreceiving areas C, L, R, LC and RC changes from (a) to (d), as shown inFIG. 9. When the Spot AF mode is in operation, the activated AF frameshifts from fa to fd when the effective pattern of positions of thelight receiving areas C, LC and RC changes from (a) to (d). With thisstructure, in either Multi-AF mode or Spot AF mode, the large differencein size between the actual light receiving range and the AF frame isalmost completely reduced, and the photographer can thus visuallyconfirm the actual size of the light receiving range at a currentlyselected focal length

The main feature of the camera 11 of the second embodiment, that ofadjusting parallax occurring between the distance measuring unit 18 andthe photographing lens 13, will be explained below with reference toFIGS. 19 to 21.

In an ideal configuration, each optical axis of the air of image forminglenses 25 and 26 of the distance measuring unit 18 is parallel to theoptical axis O of the photographing lens 13, so as not to have asubstantial parallax occurring between the distance measuring unit 18and the photographing lens 13. In FIG. 19, the optical axes of the pairof image forming lenses 25 and 26 are shown as a single optical axis "o₁" for the purpose of illustration. However, in practice, it is often thecase that the optical axis "o₁ " is not precisely set parallel to theoptical axis O of the photographing lens 13 and is thus off-set withrespect thereto, due to, for example, a slight variation in size of eachmember or element of the camera 11. In FIG. 19, an optical axis "o₁ "shown with short dotted lines, illustrates such an off-set optical axis.

According to the distance measuring apparatus to which the second aspectof the present invention is applied, the amount of parallax between thedistance measuring unit 18 and the photographing lens 13 is measured andstored in the ROM 84, during the manufacturing process, as data peculiarto the camera 11. The CPU 50 selects, in accordance with the data storedin the ROM 84, a group of light receiving elements (i.e., photodiodes)to be used for the subject distance calculating operation from a largenumber of light receiving elements provided on each of the line sensors27 and 28, to thereby adjust the parallax between the distance measuringunit 18 and the photographing lens 13 without actually moving thedistance measuring unit 18 relative to the camera body. The details ofthis will be explained below.

As shown in FIG. 20, light data received is outputted as data "A" in thecenter of an output chart OC, in the case where the optical axis "o₁ "of the distance measuring unit 18 is parallel to the optical axis O ofthe photographing lens 13. However, in many cases, the same receivedlight data is outputted as data "B", which is shifted from the center ofthe output chart OC due to the optical axis "o₁ " being somewhatdeviated from and off-set with respect to the optical axis O of thephotographing lens 13, as illustrated in FIG. 19 by "o₁ " having shortdotted lines.

In the distance measuring apparatus to which the second aspect of thepresent invention is applied, the amount of parallax between thedistance measuring unit 18 and the photographing lens 13 is regarded asthe amount data "B" deviates from data "A", i.e., the deviation amountcorresponding to the number of light receiving elements by which thelight receiving areas outputting data "B" deviates from the lightreceiving areas outputting data "A", in the horizontal direction of thecamera 11. This deviation amount is stored as data in the ROM 84 as aparallax adjusting amount a and a subject distance measurement iscarried out with the light receiving areas to be used on each of theline sensors 27 and 28 being shifted by the parallax adjusting amountα.In other words, a subject distance measurement is carried out under thecondition that the center of each of the line sensors 27 and 28, whichis to be generally located to correspond to the center C of the outputchart OC, is shifted to correspond to the position C' which is shiftedfrom the center C by the parallax adjusting amount α. The parallaxadjusting amountα may be positive (+α) or negative (-α), according tothe direction of deviation, i.e., when the light receiving areasoutputting data "B" deviates from the light receiving areas outputtingdata "A" in one direction (e.g., in the right direction of FIG. 20) orin the other direction (e.g., in the left direction of FIG. 20),respectively.

The parallax adjusting amount α is measured during the manufacture ofthe camera 11 with a line chart LC, such as shown in FIG. 19. As shownin FIG. 19, when the parallax adjusting amount α is measured, the camera11 is placed to face in the direction of the line chart LC in such amanner that the ideal optical axis "o₁ ", parallel to the optical axis Oof the photographing lens 13, of the distance measuring unit 18 isaligned with a vertical center line L printed on the line chart LC.

In order to realize a correction of parallax between the distancemeasuring unit 18 and the photographing lens 13, since the effectivelight receiving areas C, L, R, LC and RC need to be shifted together inthe right or left direction with respect to the center of each linesensor 27, 28, each line sensor 27, 28 is comprised of more than 128light receiving elements, that is, in addition to the 128 lightreceiving elements provided in the center, a predetermined number oflight receiving elements are added on each of the right and left edgesof each line sensor 27, 28. For instance, each line sensor 27, 28 may becomprised of more than 148 light receiving elements. In this particularcase, it will be understood that ten light receiving elements are addedon each of the right and left edges of each line sensor 27, 28. Thenumber of light receiving elements added on each of the right and leftedges of each line sensor 27, 28 is predetermined so as to correspond toa maximum parallax adjusting amount ±α_(max). In other words, the numberof light receiving elements added on the left edge of each line sensor27, 28 corresponds to a maximum parallax adjusting amount -α, and thenumber of light receiving elements added on the right edge of each linesensor 27, 28 corresponds to a maximum parallax adjusting amount +α.FIGS. 21(a), (b) each show line sensor 27 or 28 of the distancemeasuring unit 18 provided in the camera 11 to which the second aspectof the present invention is applied. In FIG. 21(a), the oblique-linedportion on each of the right and left edges of the line sensor shows theadditional light receiving elements, the number of which corresponds tothe above mentioned maximum parallax adjusting amount±α_(max).

The operation of the camera 11 of the second embodiment having the abovementioned circuit structure will be hereinafter discussed. The mainroutine performed by the CPU 50 is the same as that of the camera 11 ofthe first embodiment which is shown in FIGS. 11 to 13.

FIG. 22 shows a "Photographing Operation" subroutine of the camera 11 ofthe second embodiment. This subroutine is the same as that of the camera11 of the first embodiment shown in FIG. 14, except that this secondembodiment has a subroutine labelled "Subject Distance MeasuringOperation" at Step S630 before Step S64 instead of the subroutine"Multi-AF Operation" in the first embodiment. Accordingly, in the secondembodiment, when it is checked that there is no error at Step S62, thecontrol proceeds to the subroutine "Subject Distance MeasuringOperation" at Step S630. This subroutine is shown in FIG. 23.

At Step S190, the CPU 50 inputs the sensor data outputted from thedistance measuring unit 18, and subsequently, the CPU 50 inputs theparallax adjusting amount +α or -α, stored in the ROM 84 duringmanufacturing, at Step S191. Thereafter, it is checked at Step S192whether or not the Multi-AF mode is selected, and the control proceedsto a subroutine labelled "Multi-AF Operation" at Step S194 if theMulti-AF mode is selected, or to Step S193 if not selected.

At Step S193 it is checked whether or not the Spot AF mode is selected,and the control proceeds to a subroutine labelled "Spot AF Operation" atStep S195 if the Spot AF mode is selected, or to a subroutine labelled"Macro AF Operation" at Step S196 if not selected.

FIG. 24 shows the subroutine "Multi-AF Operation" at Step S194.

The four sensor start numbers, i.e., DIV 0, DIV 1, DIV 2 and DIV 3,which respectively correspond to the first, second, third and fourthranges of the zooming range of the photographing lens 13, each determinethe position of each of the light receiving areas C, L, R, LC and RC,and are stored in the RAM 83, in accordance with the information readout from the lens information reading circuit 78 when the zoomingoperation or the macro operation is performed in accordance with theoperation at Step S10, S13 or S26.

In the subroutine "Multi-AF Operation" at Step S194, under the conditionthat one set of the light receiving areas C, L, R, LC and RC to be used,which has one of the four predetermined sets of positions (a), (b), (c)and (d) (FIG. 9), has already been selected or determined in accordancewith the data of the above mentioned four sensor start numbers and thefour predetermined sets of positions (a), (b), (c) and (d) stored in theROM 84, it is checked whether or not there is a default (i.e., the statein which a subject distance value cannot be measured) at any of thelight receiving areas C, L, R, LC and RC, and among the subject distancevalues obtained with the light receiving areas each having no default,one subject distance value which is within a predetermined focus-capabledistance range and closest to the camera 11 is selected to be used forfocusing.

In the subroutine "Multi-AF Operation" at Step S194, the sensor startnumber currently stored in the RAM 83 is read and it is checked whetherthe read sensor start number is "DIV 0" or not at Step S197. The controlproceeds to Step S199 if it is judged that the read sensor start numberis "DIV 0". At Step S199, the CPU 50 inputs, from the ROM 84, theinformation regarding the read sensor start number "DIV 0", i.e., "C₋₋DIV 0", "L DIV 0", "R₋₋ DIV 0", "LC₋₋ DIV 0" and "RC₋₋ DIV 0", whoserespective positions are shown in FIG. 9(a).

Each positional information "C₋₋ DIV 0", "L₋₋ DIV 0", "R DIV 0", "LC₋₋DIV 0" and "RC₋₋ DIV 0" represents the position of the light receivingelement positioned at one end (the right end in FIG. 9) of thecorresponding light receiving area, which consists of 36 light receivingelements.

At Step S200, the CPU 50 inputs the parallax adjusting amountα stored inthe ROM 84 and the positional information "C₋₋ DIV 0", "L₋₋ DIV 0", "R₋₋DIV 0", "LC₋₋ DIV 0" and "RC₋₋ DIV 0", having been input at Step S199,are each adjusted in accordance with the input parallax adjusting amountα, and subsequently, the effective positions of the light receivingareas C, L, R, LC and RC are each determined in accordance with theabove mentioned adjusted information "C₋₋ DIV 0", "L₋₋ DIV 0", "R₋₋ DIV0", "LC₋₋ DIV 0" and "RC₋₋ DIV 0", respectively, in the followingmanner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position "C₋₋ DIV 0"±α, to the leftend. The position of the left end is determined by the amount "C₋₋ DIV0±α+(N-1)", i.e., "1±α+(N-1)". Here, as mentioned previously, "N"represents the predetermined number of light receiving elements of whicheach of the light receiving areas C, L, R, LC and RC consists, i.e., 36.When the parallax adjusting amount α is a positive value, the value +αis added to the positional information. When the parallax adjustingamount α is a negative value, the value -α is subtracted from thepositional information.

The center light receiving area C can be expressed in the range definedby "C₋₋ DIV 0±α˜C₋₋ DIV 0±α+(N-1)". The rest of the light receivingareas L, R, LC and RC are each determined in a similar manner.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 0±α", to the leftend thereof by the amount "L₋₋ DIV 0±α+(N-1)", i.e., "1±α+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 0±α", to the leftend thereof by the amount "R₋₋ DIV 0±α+(N-1)", i.e. "1±α+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 0±α", to the left endthereof by the amount "LC DIV 0±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 0±α", to the left endthereof by the amount "RC DIV 0±α+(N-1)", i.e. , "1±α+(N-1)".

The arithmetic operating portion 31 provided in the distance measuringunit 18 sends to the CPU 51, in sequence, the sensor data that isoutputted from each of the light receiving elements located on each ofthe light receiving areas C, L, R, LC and RC, in accordance with thesignals outputted from the CPU 50. For instance, in the case when it isnecessary for the CPU 50 to receive a series of sensor data from theright light receiving area R ranging from the (9±α)th light receivingelement (counted from the right end of the total 128 light receivingelements) to the left end of the right light receiving area R, thearithmetic operating portion 31 sends in sequence the sensor dataoutputted from each of the 36 light receiving elements ranging from theabove mentioned (9±α)th light receiving element to the (9±α+35)th lightreceiving element, i.e., 9±α+(36-1).

After Step S200, the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S208 in which it is checked whether thereis a default at each of the light receiving areas C, L, R, LC and RC inaccordance with the inputted sensor data.

At Step S197, if it is judged that the read sensor start number is not"DIV 0", the control proceeds to Step S198 to check if the read sensorstart number is "DIV 1". If it is judged that the read sensor startnumber is "DIV 1", the control proceeds to Step S202. At Step S202, theCPU 50 inputs from the ROM 84, the positional information regarding theread sensor start number "DIV 1", i.e., "C DIV 1", "L₋₋ DIV 1", "R₋₋ DIV1", "LC₋₋ DIV 1" and "RC₋₋ DIV 1", whose respective positions are shownin FIG. 9(b).

Thereafter, at Step S203, the CPU 50 inputs the parallax adjustingamount α stored in the ROM 84 and the positional information "C₋₋ DIV1", "L₋₋ DIV 1", "R₋₋ DIV 1", "LC DIV 1" and "RC₋₋ DIV 1", having beeninput at Step S202, are each adjusted in accordance with the inputparallax adjusting amount α. Subsequently, the effective positions ofthe light receiving areas C, L, R, LC and RC are each determined inaccordance with the above mentioned adjusted information "C₋₋ DIV 1","L₋₋ DIV 1", "R₋₋ DIV 1", "LC DIV 1" and "RC DIV 1", respectively, inthe following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position "C₋₋ DIV 1"±α, to the leftend. The position of the left end is determined by the amount "C₋₋ DIV1±α+(N-1)", i.e., "1±α+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 1±α˜C₋₋ DIV 1±α+(N-1)". Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 1±α", to the leftend thereof by the amount "L₋₋ DIV 1±α+(N-1)", i.e., "1±α+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 1±α", to the leftend thereof by the amount "R₋₋ DIV 1±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 1±α", to the left endthereof by the amount "LC₋₋ DIV 1±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 1±α", to the left endthereof by the amount "RC₋₋ DIV 1±α+(N-1)", i.e., "1±α+(N-1)",

After Step S203, the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S208.

At Step S198, if it is judged that the read sensor start number is not"DIV 1", the control proceeds to Step S201 to check if the read sensorstart number is "DIV 2". If it is judged that the read sensor startnumber is "DIV 2", the control proceeds to Step S204. At Step S204, theCPU 50 inputs, from the ROM 84, the positional information regarding theread sensor start number "DIV 2", i.e., "C DIV 2", "L₋₋ DIV 2", "R₋₋ DIV2", "LC₋₋ DIV 2" and "RC DIV 2", whose respective positions are shown inFIG. 9(c).

Thereafter, at Step S205, the CPU 50 inputs the parallax adjustingamount α stored in the ROM 84 and the positional information "C₋₋ DIV2", "L₋₋ DIV 2", "R₋₋ DIV 2", "LC DIV 2" and "RC₋₋ DIV 2" having beeninput at Step S204 are each adjusted in accordance with the inputparallax adjusting amount α. Subsequently, the effective positions ofthe light receiving areas C, L, R, LC and RC are each determined inaccordance with the above mentioned adjusted information "C₋₋ DIV 2","L₋₋ DIV 2", "R-DIV 2", "LC DIV 2" and "RC₋₋ DIV 2", respectively, inthe following manner.

The range of the center light receiving area C is determined by thewidth from the right end,. i.e., the position "C₋₋ DIV 2"±α, to the leftend. The position of the left end is determined by the amount "C₋₋ DIV2±α+(N-1)", i.e., "1±α+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 2±α˜C₋₋ DIV 2±α+(N-1)". Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 2±α", to the leftend thereof by the amount "L₋₋ DIV 2±α+(N-1)", i.e., "1±α+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 2±α" to the leftend thereof by the amount "R₋₋ DIV 2±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 2±α", to the left endthereof by the amount "LC DIV 2±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 2±α", to the left endthereof by the amount "RC DIV 2±α+(N-1)", i.e., "1±α+(N-1)".

After Step S205, the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S208.

At Step S201, if it is judged that the read sensor start number is not"DIV 2", the control proceeds to Step S206. At Step S206, the CPU 50inputs, from the ROM 84, the positional information regarding the readsensor start number "DIV 3", i.e., "C₋₋ DIV 3", "L₋₋ DIV 3", "R₋₋ DIV3", "LC DIV 3" and "RC₋₋ DIV 3", whose respective positions are shown inFIG. 9(d).

Thereafter, at Step S207, the CPU 50 inputs the parallax adjustingamount α stored in the ROM 84 and the positional information "C₋₋ DIV3", "L₋₋ DIV 3", "R₋₋ DIV 3", "LC DIV 3" and "RC₋₋ DIV 3", having beeninput at Step S206, are each adjusted in accordance with the inputparallax adjusting amount α. Subsequently, the effective positions ofthe light receiving areas C, L, R, LC and RC are each determined inaccordance with the above mentioned adjusted information "C₋₋ DIV 3","L₋₋ DIV 3", "R₋₋ DIV 3", "LC DIV 3" and "RC₋₋ DIV 3", respectively, inthe following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position "C₋₋ DIV 3"±α, to the leftend. The position of the left end is determined by the amount "C₋₋ DIV3±α+(N-1)", i.e., "1±α+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 3±α˜C₋₋ DIV 3±α+(N-1)". Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner.

The left light receiving area L is determined such that it ranges fromthe right end thereof, i.e., the position of "L₋₋ DIV 3±α", to the leftend thereof by the amount "L₋₋ DIV 3±α+(N-1)", i.e., "1±α+(N-1)".

The right light receiving area R is determined such that it ranges fromthe right end thereof, i.e., the position of "R₋₋ DIV 3±α, to the leftend thereof by the amount "R₋₋ DIV 3±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 3±α", to the left endthereof by the amount "LC DIV 3±α+(N-1)", i.e., "1±α+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 3±α", to the left endthereof by the amount "RC DIV 3±α+(N-1)", i.e., "1±α+(N-1)".

After Step S207, the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S208.

In the subroutine "Default Detecting Operation" at Step S208, it ischecked whether there is a default at each of the light receiving areasC, L, R, LC and RC, determined in accordance with the inputted sensordata, i.e., in accordance with the selected focal length of thephotographing lens 13. In accordance with the result of this checking, aflag is set to correspond to each of the determined light receivingareas having no default. For instance, in the case where the lightreceiving areas LC and RC each have a default detected while the lightreceiving areas C, L and R each have no default detected, flags arerespectively set corresponding to the light receiving areas C, L and R.

After Step S208 the control proceeds to a subroutine labelled"Arithmetic Operation" at Step S209. Here a subject distance value iscalculated for each of the light receiving areas C, L, R, LC and RC. Thecalculated subject distance values for each of the light receiving areasC, L, R, LC and RC are respectively CX, LX, RX, LCX and RCX. The largerthe subject distance value CX, LX, RX, LCX or RCX is, the closer thecorresponding subject to be photographed is located to the camera 11.

Thereafter, the control proceeds to a subroutine labelled "CalculatedSubject Distance Value Selecting Operation" at Step S210. Thissubroutine includes the same steps as Steps S98 to S119 in thesubroutine "Multi-AF Operation" shown in FIGS. 16 and 17. In thesubroutine "Calculated Subject Distance Value Selecting Operation", acertain value is obtained as the reference subject distance value "X".After this subroutine is completed the control returns.

The subroutine "Spot AF Operation" at Step S195 will be explained withreference to FIG. 25. In this subroutine, each of the light receivingareas C, L, R, LC and RC, each having been set at respective positionsof one of four sets of positions (a), (b), (c) and (d) shown in FIG. 9in accordance with a set focal length, are shifted by the parallaxadjusting amount α, and it is checked whether or not there is a default(i.e., the state in which a subject distance cannot be measured) at anyof the light receiving areas C, L, R, LC and RC. Among the subjectdistance values obtained with the light receiving areas each having nodefault, one subject distance value, which is within a predeterminedfocus-capable distance range and closest to the camera 11, is selectedto be used for focusing.

When the control enters the subroutine "Spot AF Operation" at Step S195,the light receiving areas C, L, R, LC and RC are each shifted by theparallax adjusting amount α, read out from the ROM 84, and set to beused for Spot AF at Step S211. Thereafter, the control proceeds to asubroutine labelled "Default Detecting Operation" at Step S212 in whichit is checked if there is a default at each of the light receiving areasC, LC and RC in accordance with the inputted sensor. Subsequently, thecontrol proceeds to a subroutine labelled "Subject Distance CalculatingOperation" at Step S213, in which a subject distance value of each ofthe light receiving areas C, LC and RC is calculated.

After Step S213, the control proceeds to Step S214 to check if there isa default at the center light receiving area C, and the control proceedsto Step S216 if there is no default, or to Step S215 if there is adefault. At Step S216, the subject distance value of the center lightreceiving area C is adopted as a subject distance value to be used forphotographing. At Step S215, it is checked if there is a default at boththe light receiving areas LC and RC, and the control proceeds to StepS217 if both light receiving areas have a default, or to Step S218 ifnot. At Step S217 it is judged that there is no subject distance value,i.e., no subject distance value can be obtained, and the controlreturns.

At Step S218 it is checked if there is no default at any of the lightreceiving areas LC and RC, and the control proceeds to Step S220 ifthere is no default, or to Step S219 if there is a default at either thelight receiving area LC or RC. At Step S220, the subject distance valueof the light receiving areas LC and RC which is closer to the camera 11is adopted to be used for photographing.

At Step S219 it is checked if there is a default at the light receivingarea LC, and the control proceeds to Step S222 if there is a default, orto Step S221 if there is no default. At Step S222 the subject distancevalue of the light receiving area RC is adopted as a subject distancevalue to be used for photographing, while the subject distance value ofthe light receiving area LC is adopted as a subject distance value to beused for photographing, at Step S221. The control returns after thecompletion of either Step S221 or Step S222.

As can be understood from the foregoing, according to the camera 11having a distance measuring apparatus to which the second aspect of thepresent invention is applied, the parallax between the the distancemeasuring unit 18 and the photographing lens 13 can be adjusted withoutactually moving the distance measuring unit 18 relative to the camerabody for adjustment. Accordingly, the adjusting operation can besimplified.

Another embodiment (i.e., a third embodiment) of a camera to which adistance measuring apparatus according to a third aspect of the presentinvention is applied will be discussed below. The camera of the thirdembodiment is similar to the cameras of the first and secondembodiments, except in several respects, and it is only to thesedifferences that the following discussion will cover. The camera of thethird embodiment will be explained below in reference to FIGS. 1˜9,11˜13, 15˜18, 26˜31.

Although the finder LCD 57 of the camera 11 of the first embodiment iscapable of indicating only the AF frames Fa, Fb, Fc and Fd, as shown inFIG. 10, the finder LCD 57 of the camera 11 of this third embodiment isthe same as that of the camera 11 of the second embodiment, that is,capable of further indicating, inside the AF frame Fa, four additionalAF frames fa, fb, fc and fd. The AF frames fa, fb, fc and fd areeffectively utilized when the "Spot AF" is carried out. The control ofthe finder LCD 57 in the Spot AF mode in the camera 11 of this thirdembodiment is identical to that in the camera 11 of the secondembodiment.

The camera 11 includes a macro photography mode (i.e., Macro mode) inaddition to a regular photography mode. The Macro mode may be selectedby a photographer operating the macro switch 46. In the camera 11 of thethird embodiment, the AF frame fd is not only used as an AF framecorresponding to the telephoto extremity in the Spot AF mode, but alsoan AF frame used in the Macro mode. When the Macro mode is selected,only the AF frame fd is activated to become visible, i.e., turned ON,and the rest of the AF frames Fa, Fb, Fd, Fc, fa, fb and fc are allturned OFF.

It should be noted that the optical axis of the finder provided in thecamera 11 has been adjusted to be parallel to the optical axis O of thephotographing lens 13, so as not to have a substantial parallaxoccurring between the finder and the photographing lens 13.

The main feature of the camera 11 of the third embodiment, i.e., forcorrecting a difference between the position of the AF frame fd in thefinder view 47 and the actual light receiving area of each of the linesensors 27 and 28 when the Macro mode is selected, will be explainedbelow.

The distance measuring unit 18 is generally fixed to the camera 11 sothat each optical axis of the pair of image forming lenses 25 and 26 ofthe distance measuring unit 18 may be parallel to the optical axis O ofthe photographing lens 13, as shown in FIG. 26. In FIG. 26, the opticalaxes of the pair of image forming lenses 25 and 26 are shown as a singleoptical axis "o" for the purpose of illustration. Due to thisconfiguration, a large difference or gap occurs between the position oneach of the line sensors 27 and 28 on which the subject light isincident when the subject is located apart from the camera 11 by apredetermined distance, e.g., in a range "b" of the regular photographymode shown in FIG. 26, and when the subject is located quite close tothe camera 11, e.g., in a range "a" of the Macro mode shown in FIG. 26.Therefore, in a conventional camera, the position of an AF frame in afinder view and the light receiving area of each of the two line sensorsdo not properly correspond to each other, especially in the Macro mode.

In order to overcome the aforementioned problem, according to the thirdaspect of the present invention, the amount of variation or shift of twolight receiving areas, i.e., the first light receiving area on each ofthe line sensors 27 and 28 on which light of the subject located withinthe range "b" of the regular photography mode is incident and the secondlight receiving area on each of the line sensors 27 and 28 on whichlight of the subject located within the range "a" of the Macro mode isincident, is stored in the ROM 84, during manufacturing, as a variationadjusting data (i.e., information C₋₋ MAC, LC₋₋ MAC, RC₋₋ MAC regardingthe sensor start number). When the photography mode is changed from theregular photography mode to the Macro mode, a group of light receivingelements (i.e., photodiodes) to be used for macro photography isselected among a large number of light receiving elements in each of theline sensors 27 and 28, in accordance with the variation adjusting datastored in the ROM 84. Namely, when the Macro mode is selected by aphotographer using the macro switch 46, the CPU 50 automatically changesthe light receiving areas of each line sensor 27, 28 which are used forthe regular photography mode to those for the Macro mode, which isillustrated in FIG. 27.

In the regular photography mode, the light receiving areas C, LC and RCare respectively located at their normal positions as a group of lightreceiving areas "D" shown in FIG. 27. When the light receiving areas C,LC and RC of the group D receive subject light, the received light datais outputted as data "A" about the center of the output chart OC.However, in the Macro photographing mode, the light receiving areas C,LC and RC are respectively located at a position shifted to the left ofthe normal position by a predetermined amount, as a group of lightreceiving areas "E", shown in FIG. 27. The predetermined amount of shiftcorresponds to the amount of parallax between the optical axis "O" ofthe line sensors 27, 28 and the optical axis of the photographing lens13. When the light receiving areas C, LC, RC of the group E receivesubject light, the received light data is thus outputted as data "B" ata position shifted to the left of data "A". In other words, as shown inFIG. 28, the center of an effective set of light receiving areas C, LCand RC used for the regular photography mode that is located on a "G"line in the regular photography mode is shifted to the left by apredetermined number of light receiving elements.

In either FIG. 27 or 28, only three light receiving areas C, LC and RCare shown on each line sensor 27, 28. This is because Spot AF isperformed for measuring a subject distance in the Macro mode, thus theother light receiving areas L and R are not used in the Macro mode.

The operation of the camera 11 of the third embodiment having the abovementioned circuit structure will be hereinafter discussed. The mainroutine performed by the CPU 50 is the same as that of the camera 11 ofthe first embodiment which is shown in FIGS. 11 to 13.

In the camera 11 of the third embodiment, the subroutine "PhotographingOperation" of FIG. 14 is replaced by that shown in FIG. 29. Steps commonto both flow charts are designated by like numerals and explanations forthese steps are omitted (on the whole).

Prior to Step S64 a subroutine labelled "Subject Distance MeasuringOperation" is carried out at Step S363. This subroutine is shown in FIG.30 and is substantially the same as the subroutine "Subject DistanceMeasuring Operation" of the camera 11 of the second embodiment shown inFIG. 23, except that the subroutine shown in FIG. 30 does not have StepS191. Steps common to both flow charts have like reference numerals andexplanations for these steps are omitted. After Step S363, the controlproceeds to Step S64, then to Step S65, and subsequently, to Step S346.

At Step S346 it is checked if the Macro mode has been selected, and thecontrol proceeds to Step S347 if the macro mode has been selected or toStep S67 it has not. At Step S67 it is checked if a subject distancevalue which can be used for photographing has been calculated (i.e., ifthere is any error in the subject distance calculation).

At Step S347 if it is judged that a subject distance value which can beused for photographing has not been calculated (i.e., there is someerror in the subject distance calculation), the control proceeds to StepS71 to make the green light emitter 12b blink so as to inform thephotographer that an in-focus state cannot be obtained. Conversely, atStep 5347 if it is judged that a subject distance value which can beused for photographing has been calculated (i.e., there is no error inthe subject distance calculation), the control proceeds to Step S348 toturn the green light emitter 12b ON so as to inform the photographerthat an in-focus state has been obtained.

The subroutine "Multi-AF Operation" at Step S194 shown in FIG. 30 is thesame as that of the camera 11 of the first embodiment shown in FIGS. 16and 17. In the subroutine "Multi-AF Operation" at Step S194 shown inFIG. 30, the four sensor start numbers, i.e., DIV 0, DIV 1, DIV 2 andDIV 3, which respectively correspond to the first, second, third andfourth ranges of the zooming range of the photographing lens 13, eachdetermine the position of each of the light receiving areas C, L, R, LCand RC, and are stored in the RAM 83 in accordance with the informationread out from the lens information reading circuit 78 when the zoomingoperation or the macro operation is performed in accordance with theoperation at Step S10, S13 or S26.

The subroutine "Macro AF Operation" at Step S196 shown in FIG. 30 isshown in FIG. 31. This subroutine "Macro AF Operation" will behereinafter discussed.

In the subroutine "Macro AF Operation", a set of light receiving areason each line sensor 27, 28 which is used in the regular photography modeis shifted by a predetermined amount for the Macro mode, thereby precisesubject distance measuring can be achieved in the Macro mode even whenthe optical axis "o" of the distance measuring unit 18 is deviatedlargely from the optical axis "O" of the photographing lens 13 in thehorizontal direction of the camera 11.

When the control enters the subroutine "Macro AF Operation" shown inFIG. 31, the CPU 50 inputs, from the ROM 84, the information regardingthe read sensor start number, i.e., "C₋₋ MAC", "LC₋₋ MAC" and "RC₋₋ MAC"(i.e., variation adjusting data), at Step S323. Thereafter, at StepS324, the positions of the light receiving areas C, LC and RC are eachdetermined in accordance with the above mentioned information "C₋₋ MAC","LC₋₋ MAC" and "RC₋₋ MAC", respectively, in the following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position "C₋₋ MAC", to the left end.The position of the left end is determined by the amount "C₋₋MAC"+(N-1), i.e., "1+(N-1)". Here, "N" represents the predeterminednumber of light receiving elements of which each of the light receivingareas C, LC and RC consists, i.e., 36. The center light receiving area Ccan be expressed in the range defined by "C₋₋ MAC"˜"C₋₋ MAC"+(N-1). Therest of the light receiving areas LC and RC are each determined in asimilar manner.

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the Position of "LC₋₋ MAC", to the left endthereof by the amount "LC₋₋ MAC"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ MAC", to the left endthereof by the amount "RC₋₋ MAC"+(N-1), i.e., "1+(N-1)".

After Step S324 the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S325. At Step S325 it is checked whetherthere is a default at each of the light receiving areas C, LC and RC,determined for the Macro mode.

In accordance with the result of this checking at Step S325, a flag isset to correspond to each of the determined light receiving areas havingno default. For instance, in the case where the light receiving area LChas a default detected while the light receiving areas C and RC eachhave no default detected, flags are respectively set corresponding tothe light receiving areas C and RC.

After Step S325, the control proceeds to a subroutine labelled"Arithmetic Operation" at Step S326. Here a subject distance value iscalculated for each of the light receiving areas C, LC and RC. Thecalculated subject distance values for each of the light receiving areasC, LC and RC are respectively CX, LCX and RCX. The larger the subjectdistance value CX, LCX or RCX is, the closer the corresponding subjectto be photographed is located to the camera 11.

After the subroutine "Arithmetic Operation" at Step S326, it is judged,in turn, whether there is any default at each of the light receivingareas C, LC and RC determined for the Macro mode, and whether each ofthe calculated subject distance values CX, LCX and RCX are within aphotographable range, e.g., the macro photography range "a" shown inFIG. 26.

Firstly, at Step S327, it is checked whether there is no default at thelight receiving area C and whether the calculated subject distance valueCX is within the photographable range, and the control proceeds to StepS328 if there is no default at the light receiving area C and thecalculated subject distance value CX is within the photographable range.At Step S328 the calculated subject distance value CX is adopted as aneffective subject distance value to be used for a focusing operation,and thereafter the control returns to the calling routine. At Step S327,if it is determined that there is a default at the light receiving areaC and/or the calculated subject distance value CX is out of thephotographable range, the control proceeds to Step S329.

At Step S329 it is checked if there is no default at the light receivingareas LC and RC, and the control proceeds to Step S331 if there is nodefault, or to Step S330 if there is default at at least one of thelight receiving areas LC, RC.

At Step S331 it is checked whether both the calculated subject distancevalues LCX and RCX are out of the photographable range, and the controlproceeds to Step S332 if both are out of the photographable range. AtStep S332 it is judged that there is no calculated subject distancevalue and thereafter the control returns. At Step S331 if either thecalculated subject distance value LCX or RCX is within thephotographable range, the control proceeds to Step S333 where thereference subject distance value "X" is set to "0" (zero) as an initialvalue. Thereafter the control proceeds to Step S334.

At Step S334, it is checked if the calculated subject distance value LCXis within the photographable range, and the control proceeds to StepS335 if within the photographable range, or to Step S336 if not. At StepS335 the reference subject distance value "X" is replaced by thecalculated subject distance value LCX. Thereafter the control proceedsto Step S336.

At Step S336, it is checked if the calculated subject distance value RCXis within the photographable range, and, if so, the control proceeds toStep S337, or the control returns if the subject distance is not withinthe photographable range. At Step S337 it is checked if the calculatedsubject distance value RCX is larger than the reference subject distancevalue "X", and, if yes, the control proceeds to Step S338, or thecontrol returns if the value of the calculated subject distance valueRCX is equal to or smaller than the reference subject distance value"X". At Step S338 the reference subject distance value "X" is replacedby the calculated subject distance value RCX, and thereafter, thecontrol returns.

At Step S330, it is checked if there is a default at both the lightreceiving areas LC and RC, and, if so, the control proceeds to StepS339, or to Step S340 if not. At Step S339 it is judged that there is nocalculated subject distance value and thereafter the control returns.

At Step S340 it is checked if there is a default at the light receivingarea LC, and, if so, the control proceeds to Step S342, otherwisecontrol proceeds to step S341. At Step S342 it is checked if thecalculated subject distance value RCX is within the photographablerange, and, if so, the control proceeds to Step S343, or if not, to StepS345. At Step S343 the reference subject distance value "X" is replacedby the calculated subject distance value RCX. Thereafter the controlreturns. At Step S345 it is judged that there is no calculated subjectdistance value and thereafter the control returns.

At Step S341 it is checked if the calculated subject distance value LCXis within the photographable range, and the control proceeds to StepS344 if the value LCX is within this range, or to Step S345 if not. AtStep S344 the reference subject distance value "X" is replaced by thecalculated subject distance value LCX. Thereafter the control returns.

According to the operations from Step S327 to Step S345, a certain valueis obtained as the reference subject distance value "X". At Step S347shown in FIG. 29 it is checked whether this obtained value is greaterthan "0" (zero). If the value is equal to or less than "0", it meansthat a subject distance value usable for a focusing operation has notbeen calculated (i.e., an in-focus state cannot be obtained). In thiscase, the control proceeds to Step S71 to make the green light emitter12b blink so as to inform the photographer that an in-focus state cannotbe obtained.

Conversely at Step S347, when the obtained value is greater than "0", itmeans that a subject distance value usable for a focusing operation hasbeen calculated (i.e., an in-focus state has been obtained). In thiscase, the control proceeds to Step S348 and the green light emitter 12bis lit so as to inform the photographer that an in-focus state has beenobtained.

As can be understood from the foregoing, in the third embodiment ofcamera 11 having a distance measuring apparatus to which the thirdaspect of the present invention is applied, when the Macro mode isselected, the actual light receiving area on each of the line sensors 27and 28 is varied or adjusted to correspond to the AF frame for macrophotography in the finder view 47. Thus, according to the thirdembodiment the subject or subjects seen within the AF frame fd isprecisely focused in a reliable manner, and the chances of the distanceof a subject, that a photographer does not intend to photograph, beingmistakenly measured as the distance of a main subject are greatlyreduced.

As can be seen from the foregoing, according to the camera having adistance measuring apparatus to which the third aspect of the presentinvention is applied, since the light receiving area on each of the pairof line sensors is varied or adjusted to correspond to the macro AFframe seen in the finder view when the Macro mode is selected, a subjector subjects seen within the macro AF frame is precisely and reliablyfocused, and furthermore, the chance of the distance of a subject, thata photographer does not intend to photograph, being mistakenly measuredas the distance of a main subject is greatly reduced.

Another embodiment (i.e., a fourth embodiment) of a camera to which adistance measuring apparatus according to a fourth aspect of the presentinvention is applied will be discussed below. The camera of the fourthembodiment is similar to the camera of the first embodiment except inseveral respects. Furthermore, some aspects of the camera of the fourthembodiment are the same as those of the camera of the second or thirdembodiment. For this reason, only those aspects unique to the camera ofthe fourth embodiment will be discussed below with reference to FIGS.1˜9, 11˜13, 15˜18, 22, 30, 32, 33 and 34.

Although the finder LCD 57 of the camera 11 of the first embodiment iscapable of indicating only the AF frame Fa, Fb, Fc and Fd, as shown inFIG. 10, the finder LCD 57 of the camera 11 of this fourth embodiment issimilar to that of the camera 11 of the second or third embodiment, thatis, capable of further indicating, inside the AF frame Fa, fouradditional AF frames fa, fb, fc and fd. The AF frames fa, fb, fc and fdare effectively utilized when "Spot AF" is carried out. The control ofthe finder LCD 57 in the Spot AF mode in the camera 11 of the fourthembodiment is identical to that in the camera 11 of the secondembodiment.

In the camera 11 of the first embodiment, for Multi-AF, the fourpredetermined sets of positions (a), (b), (c) and (d) as shown in FIG. 9are each stored in the ROM 84. In the camera 11 of the fourthembodiment, in addition to the four sets of positions of light receivingareas for Multi-AF, another four sets of positions of light receivingareas for Spot AF are each stored in the ROM 84 as four predeterminedsets of positions (a), (b), (c) and (d), as shown in FIG. 32.

When the Spot AF mode is selected by the mode selecting switch 41, theCPU 50 selects one of the four sets (patterns) of positions (a), (b),(c) or (d) (FIG. 32) which corresponds to the focal length rangeinformation of the photographing lens 13 stored in the RAM 83, inaccordance with the position data of the light receiving areas, readfrom the ROM 84. Thereafter, the CPU 50 receives the set of signals(i.e., distance information) of the selected pattern of positions (a),(b), (c) or (d) from the arithmetic operating portion 31 and calculatesa subject distance in accordance with the set of signals.

In the camera 11 of the fourth embodiment, in the case when the Spot AFmode is selected by the mode selecting switch 41, in a similar manner tothe case when the Multi-AF mode is selected by the mode selecting switch41, the focal length variable range (i.e., zooming range) of thephotographing lens 13 is divided into four ranges, namely, first,second, third and fourth ranges, in respective order from the wide-angleextremity to the telephoto extremity. The control of the camera 11varies the positions of the light receiving areas LC and RC relative tothe position of the center light receiving area C in such a manner asshown in FIG. 32, in accordance with a variation of focal length by thezooming operation. Namely, the CPU 50 selects one of the predeterminedpatterns of positions of light receiving areas on each line sensor 27,28, i.e., the patterns of positions (a), (b), (c) or (d) as shown inFIG. 32, in accordance with the data regarding focal length rangeinformation stored in RAM 83, when a focal length is varied by thezooming operation. Although the positions of the light receiving areasLC and RC shift relative to the position of the center light receivingarea C when one pattern of positions (a), (b), (c) or (d) is changed toanother pattern in the Spot AF mode, each light receiving area is alwayscomprised of 36 light receiving elements.

The main feature of the camera 11 of the fourth embodiment, i.e., forevaluating or grading the sensor data outputted from each lightreceiving area in the case where a subject distance value is measured byusing a plurality of light receiving areas, will be explained below.

In the camera 11 of the fourth embodiment, the CPU 50 is provided withthree functions for Spot AF. The first function is a subject distancevalue calculating means to perform a subject distance value calculationfor each of the light receiving areas C, LC and RC by using sets ofsignals inputted from the respective light receiving areas C, LC and RCto thereby obtain respective subject distance values. The secondfunction is a reliability judging means to judge whether there isreliability (i.e., there is no default) in each of the three subjectdistance values of the respective light receiving areas C, LC and RC ina predetermined order. The third function is a decision means fordeciding to adopt the subject distance value of one of the lightreceiving areas C, LC and RC (firstly judged by the reliability judgingmeans that there is no default), as an effective subject distance valueto be used for focusing. The above three functions are performed onlywhen the Spot AF mode is selected.

In the ROM 84, the data is programmed for making the CPU 50 judgewhether there is reliability in each of the three subject distancevalues of the respective light receiving areas C, LC and RC in apredetermined order, i.e., in the order of, firstly, the subjectdistance value of the light receiving area C, secondly, the subjectdistance value of the light receiving area LC, and thirdly, the subjectdistance value of the light receiving area RC. The detail of thiscontrol will be discussed later in reference to FIGS. 33 and 34.

Although the CPU 50 operates the above three functions only when theSpot AF mode is selected in the camera 11 of the fourth embodiment, theCPU 50 may operate the above three functions not only in the Spot AFmode, but also in the Multi-AF mode.

In this case, in the Multi-AF mode, the first function is to perform asubject distance value calculation for each of the light receiving areasC, R, L, LC and RC by using sets of signals inputted from lightreceiving areas C, L, R, LC and RC to obtain respective subject distancevalues. The second function is to judge, in a predetermined order,whether there is reliability in each of the five subject distance valuesof the respective light receiving areas C, L, R, LC and RC. The thirdfunction is to adopt the subject distance value of one of the lightreceiving areas C, L, R, LC and RC, that is firstly judged by thereliability judging means to have no default, as an effective subjectdistance value to be used for focusing. Furthermore, in this optionalcase, in the ROM 84, the data programmed for making the CPU 50 judgewhether there is reliability in each of the five subject distance valuesof the respective light receiving areas C, L, R, LC and RC in apredetermined order, e.g., in the order of, firstly, the subjectdistance value of the light receiving area C, secondly, the subjectdistance value of the light receiving area L, thirdly, the subjectdistance value of the light receiving area R, fourthly, the subjectdistance value of the light receiving area LC, and fifthly, the subjectdistance value of the light receiving area RC.

The operation of the camera 11 of the fourth embodiment, having theabove mentioned circuit structure, will be hereinafter discussed. Themain routine performed by the CPU 50 is the same as that of the camera11 of the first embodiment which is shown in FIGS. 11 to 13.

In the camera 11 of the fourth embodiment, in the subroutine"Photographing Operation" at Step S56 in the main routine, thesubroutine "Photographing Operation" shown in FIG. 22 in the camera 11of the second embodiment is performed. Furthermore, in the camera 11 ofthe fourth embodiment, in the subroutine "Subject Distance MeasuringOperation" at Step S630 shown in FIG. 22, the subroutine "SubjectDistance Measuring Operation" shown in FIG. 30 in the camera 11 of thethird embodiment is performed. Still furthermore, in the camera 11 ofthe fourth embodiment, in the subroutine "Multi-AF Operation" at StepS194 in the "Subject Distance Measuring Operation" in FIG. 30, thesubroutine "Multi-AF Operation" shown in FIGS. 16 and 17 in the camera11 of the first embodiment is performed. Still furthermore, in thecamera 11 of the fourth embodiment, in the subroutine "Spot AFOperation" at Step S195 in the "Subject Distance Measuring Operation" inFIG. 30, the subroutine "Spot AF Operation" shown in FIGS. 33 and 34 isperformed.

The subroutine "Spot AF Operation" shown in FIGS. 33 and 34 will behereinafter explained. In this subroutine, under the condition that oneset of the light receiving areas C, LC and RC to be used, which has oneof the four predetermined sets of positions (a), (b), (c) and (d) (FIG.32), has already been selected or determined in accordance with the dataof the above mentioned four sensor start numbers and the fourpredetermined sets of positions (a), (b), (c) and (d) stored in the ROM84, it is checked whether there is reliability (i.e., there is nodefault) at each of the light receiving areas C, LC and RC in the abovementioned predetermined order. The subject distance value of one of thelight receiving areas C, LC and RC, that is firstly judged to havereliability, is adopted as an effective subject distance value to beused in a focusing operation. In this fourth embodiment, in the Spot AFmode, only the respective subject distance values of the light receivingareas C, LC and RC (not of the light receiving areas L and R), arejudged for reliability. The four sensor start numbers, i.e., DIV 0, DIV1, DIV 2 and DIV 3, which respectively correspond to the first, second,third and fourth ranges of the zooming range of the photographing lens13, and each determine the position of each of the light receiving areasC, LC and RC in the Spot AF mode, are stored in the RAM 83 in accordancewith the information read out from the lens information reading circuit78 when the zooming operation or the macro operation is performed inaccordance with the operation at Step S10, S13 or S26.

In the subroutine "Spot AF Operation" at Step S195, firstly, the sensorstart number currently stored in the RAM 83 is read and it is checked ifthe read sensor start number is "DIV 0" or not at Step S430. The controlproceeds to Step S431 if it is judged that the read sensor start numberis "DIV 0". At Step 5431, the CPU 50 inputs, from the ROM 84, theinformation regarding the read sensor start number "DIV 0", i.e., "C₋₋DIV 0", "LC₋₋ DIV 0" and "RC₋₋ DIV 0", whose respective positions areshown in FIG. 32(a).

Each positional information "C₋₋ DIV 0", "LC₋₋ DIV 0" and "RC₋₋ DIV 0"represents the position of the light receiving element positioned at oneend (the right end in FIG. 32) of the corresponding light receivingarea, which consists of 36 light receiving elements (i.e., photodiodes).

At Step S432, the positions of the light receiving areas C, LC and RCare each determined in accordance with the above mentioned information"C₋₋ DIV 0", "LC₋₋ DIV 0" and "RC₋₋ DIV 0", respectively, in thefollowing manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position "C₋₋ DIV 0", to the leftend. The position of the left end is determined by the amount "C₋₋ DIV0"+(N-1), i.e., "1+(N-1)". Here, "N" represents the predetermined numberof light receiving elements of which each of the light receiving areasC, L, R, LC and RC consists, i.e., 36 in this embodiment. The centerlight receiving area C can be expressed in the range defined by "C₋₋ DIV0" "C₋₋ DIV 0"+(N-1). The rest of the light receiving areas, LC and RC,are each determined in a similar manner.

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 0", to the left endthereof by the amount "LC DIV 0"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 0", to the left endthereof by the amount "RC₋₋ DIV 0"+(N-1), i.e., "1+(N-1)".

The arithmetic operating portion 31 provided in the distance measuringunit 18 sends, in sequence, the sensor data that is outputted from eachof the light receiving elements located on each of the light receivingareas C, LC and RC, determined in accordance with the signals outputtedfrom the main CPU 50. For instance, in the case when it is necessary forthe main CPU 50 to receive a series of sensor data from the right lightreceiving area R ranging from the 9th light receiving element (countedfrom the right end of the total 128 light receiving elements) to theleft end of the right light receiving area R, the arithmetic operatingportion 31 sends to the CPU 50, in sequence, the sensor data outputtedfrom each of the 36 light receiving elements ranging from the abovementioned 9th light receiving element to the 44th light receivingelement (i.e., 9+(36-1)), in accordance with the signals outputted fromthe main CPU 50.

After Step S432, the control proceeds to a subroutine labelled "DefaultDetecting Operation" at Step S433 in which it is checked whether thereis a default at each of the light receiving areas C, LC and RC inaccordance with the inputted sensor data.

At Step S430, if it is judged that the read sensor start number is not"DIV 0", the control proceeds to Step S434 to check if the read sensorstart number is "DIV 1". If it is judged that the read sensor startnumber is "DIV 1", the control proceeds to Step S435. At Step S435, theCPU 50 inputs from the ROM 84, the positional information regarding theread sensor start number "DIV 1", i.e., "C DIV 1", "LC₋₋ DIV 1" and"RC₋₋ DIV 1", whose respective positions are shown in FIG. 32(b).

Thereafter, at Step S436, the positions of the light receiving areas C,LC and RC are each determined in accordance with the above mentionedinformation "C₋₋ DIV 1", "LC₋₋ DIV 1" and "RC₋₋ DIV 1", respectively, inthe following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position of "C₋₋ DIV 1", to the leftend. The position of the left end is determined by the amount "C₋₋ DIV1"+(N-1), i.e., "1+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 1"˜"C₋₋ DIV 1"+(N-1). Therest of the light receiving areas LC and RC are each determined in asimilar manner.

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 1", to the left endthereof by the amount "LC₋₋ DIV 1"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 1", to the left endthereof by the amount "RC₋₋ DIV 1"+(N-1), i.e., "1+(N-1)".

After Step S436 the control proceeds to the subroutine "DefaultDetecting Operation" at Step S433.

At Step S434, if it is judged that the read sensor start number is not"DIV 1", the control proceeds to Step S437 to check if the read sensorstart number is "DIV 2". If it is judged that the read sensor startnumber is "DIV 2", the control proceeds to Step S438. At Step S438, theCPU 50 inputs, from the ROM 84, the positional information regarding theread sensor start number "DIV 2", i.e., "C DIV 2", "LC₋₋ DIV 2" and"RC₋₋ DIV 2", whose respective positions are shown in FIG. 32(c).

Thereafter, at Step S439, the positions of the light receiving areas C,LC and RC are each determined in accordance with the above mentionedinformation "C₋₋ DIV 2", "LC₋₋ DIV 2" and "RC₋₋ DIV 2", respectively, inthe following manner.

The center light receiving area C is determined by the width from theright end, i.e., the position of "C₋₋ DIV 2", to the left end. Theposition of the left end is determined by the amount "C₋₋ DIV 2"+(N-1),i.e., "1+(N-1)". The center light receiving area C can be expressed inthe range defined by "C₋₋ DIV 2"˜"C₋₋ DIV 2"+(N-1). The rest of thelight receiving areas LC and RC are each determined in a similar manner,as follows.

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 2", to the left endthereof by the amount "LC₋₋ DIV 2"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 2", to the left endthereof by the amount "RC₋₋ DIV 2"+(N-1), i.e., "1+(N-1)".

After Step S439 the control proceeds to the subroutine "DefaultDetecting Operation" at Step S433.

At Step S437, if it is judged that the read sensor start number is not"DIV 2", the control proceeds to Step S440. At Step S440, the CPU 50inputs, from the ROM 84, the positional information regarding the readsensor start number "DIV 3", i.e., "C₋₋ DIV 3", "LC₋₋ DIV 3" and "RC₋₋DIV 3", whose respective positions are shown in FIG. 32(d).

Thereafter, at Step S441, the positions of the light receiving areas C,LC and RC are each determined in accordance with the above mentionedinformation "C₋₋ DIV 3", "LC₋₋ DIV 3" and "RC₋₋ DIV 3", respectively, inthe following manner.

The range of the center light receiving area C is determined by thewidth from the right end, i.e., the position of "C₋₋ DIV 3", to the leftend. The position of the left end is determined by the amount "C₋₋ DIV3"+(N-1), i.e., "1+(N-1)". The center light receiving area C can beexpressed in the range defined by "C₋₋ DIV 3"˜"C₋₋ DIV 3"+(N-1). Therest of the light receiving areas L, R, LC and RC are each determined ina similar manner as follows.

The light receiving area LC is determined such that it ranges from theright end thereof, i.e., the position of "LC₋₋ DIV 3", to the left endthereof by the amount "LC₋₋ DIV 3"+(N-1), i.e., "1+(N-1)".

The light receiving area RC is determined such that it ranges from theright end thereof, i.e., the position of "RC₋₋ DIV 3", to the left endthereof by the amount "RC₋₋ DIV 3+(N-1), i.e., "1+(N-1)".

After Step S441 the control proceeds to the subroutine "DefaultDetecting Operation" at Step S433.

It should be noted here that, as shown in FIG. 32, as the photographinglens is moved from the wide-angle extremity to the telephoto extremity,the light receiving area C is not shifted at all on each line sensor 27,28. However, the light receiving areas LC and RC are gradually shiftedtoward a more central position, i.e., the number of overlapped lightreceiving elements increases. Note, however, that each light receivingarea always consists of 36 light receiving elements.

In the subroutine "Default Detecting Operation" at Step S433, it ischecked whether there is a default at each of the light receiving areasC, LC and RC, determined in accordance with the inputted sensor data,i.e., in accordance with the selected focal length of the photographinglens 13. In accordance with the result of this checking, a flag is setto correspond to each of the determined light receiving areas having nodefault. For instance, in the case where the light receiving areas LCand RC each have a default detected while the light receiving area C hasno default detected, a flag is set corresponding to the light receivingarea C.

After Step S433 the control proceeds to a subroutine labelled"Arithmetic Operation" at Step S442. At step S442 a subject distancevalue is calculated for each of the light receiving areas C, LC and RC.The calculated subject distance values for each of the light receivingareas C, LC and RC are respectively CX, LCX and RCX. The larger thesubject distance value CX, LCX or RCX is, the closer the correspondingsubject to be photographed is located to the camera 11.

After Step S442 the control proceeds to Step S443. At Step S443, thereference subject distance value "X" is set "0" (zero) as an initialvalue.

Thereafter, at Step S444 it is checked if there is a default at thelight receiving area C. Here it is checked whether a flag is set tocorrespond to the light receiving area C. The control proceeds to StepS445 if there is no default at the light receiving area C, or to StepS446 if there is a default at the light receiving area C. At Step S445,the reference subject distance value "X" is replaced by the value of thesubject distance value CX, and thereafter, the control returns.

At Step S446 it is checked if there is a default at both the lightreceiving areas LC and RC, where it is checked whether a flag is set tocorrespond to the light receiving area LC and whether a flag is set tocorrespond to the light receiving area RC. The control proceeds to StepS447 if there is a default at both of the light receiving areas LC, RC,or to Step S448 if there is no default at at least one of the lightreceiving areas LC, RC.

At Step S447, if it is judged that there is no subject distance value,i.e., no subject distance value could be obtained, the control returnsto enter the subroutine "Photographing Operation" shown in FIG. 22.Thereafter, if it is judged at Step S67 that there is a default, thecontrol proceeds to Step S71 to make the green light emitter 12b blinkso as to inform the photographer that an in-focus state cannot beobtained.

At Step S446, if there is no default at at least one of the lightreceiving areas LC, RC, the control proceeds to Step S448 to check ifthere is no default at both of the light receiving areas LC, RC, andthereafter, the control proceeds to Step S449 if both light receivingareas LC, RC have no default, or to Step S452 if there is a default ateither the light receiving area LC or RC.

At Step S449 the reference subject distance value "X" is replaced by thevalue of the subject distance value LCX, and thereafter, the controlproceeds to Step S450 to check if the calculated subject distance valueRCX is greater than the reference subject distance value "X". Thecontrol proceeds to Step S451 if the calculated subject distance valueRCX is greater than the reference subject distance value "X", or returnsif the calculated subject distance value RCX is equal to or smaller thanthe reference subject distance value "X". In this case when the controlreturns at Step S450, the subject distance value LCX is used in thefocusing operation as the reference subject distance value.

At Step S451 the reference subject distance value "X" is replaced by thesubject distance value RCX, and thereafter, the control returns.Consequently, the subject distance value RCX is used in the focusingoperation as the reference subject distance value.

At Step S448, if it is judged that there is a default at either lightreceiving area LC or RC, the control proceeds to Step S452 to check ifthere is a default at the light receiving area LC. Subsequently, thecontrol proceeds to Step S454 if there is a default at the lightreceiving area LC, or proceeds to Step S453 if not.

At Step S453 the reference subject distance value "X" is replaced by thesubject distance value LCX, and thereafter, the control returns.Consequently, the subject distance value LCX is used for focusing as thereference subject distance value. At Step S454 the reference subjectdistance value "X" is replaced by the subject distance value RCX, andthereafter, the control returns. Consequently, the subject distancevalue RCX is used in the focusing operation as the reference subjectdistance value.

As can be understood from the foregoing, according to the camera 11having a distance measuring apparatus to which the fourth aspect of thepresent invention is applied, even if there occurs a default at thecenter light receiving area C in the Spot mode, the value of the subjectdistance value of either light receiving area LC or RC is immediatelyadopted as an effective value in the focusing operation in a promptmanner if there is not a default at at least one of the light receivingareas LC, RC. Accordingly, not only can correct focusing be carried outbut also a subject distance value can be detected quickly, thus leadingto a fast photographing operation.

The following discussion will be addressed to another embodiment (i.e.,a fifth embodiment) of a camera to which a distance measuring apparatusaccording to a fifth aspect of the present invention is applied withreference to FIGS. 35 through 56.

FIGS. 35 and 36 respectively show a front elevational view and a backview of a lens-shutter type camera having a strobe incorporated therein,to which the fifth aspect of the present invention is applied. Thelens-shutter type camera has a camera body 111 which is provided on thefront thereof with a zoom lens 113, a photometering window 115, an AFauxiliary light emitting window 116, a finder window 117, a lightreceiving window 118 and a strobe light emitter 119. Behind the lightreceiving window 118 are placed a pair of image forming lenses 152L and152R of a distance measuring unit 151(see FIG. 38). The photometeringwindow 115, the AF auxiliary light emitting window 116, the finderwindow 117, the light receiving window 118 and the strobe light emitter119 are arranged in this order from the left as viewed in FIG. 35, andare all positioned above the zoom lens 113. There are also provided aphotometering sensor, an AF auxiliary light emitting element, a finderoptical system and a distance measuring unit 151 which are all withinthe camera body 111 behind the respective elements 115 through 119, asis well known.

A release button 121 and a strobe button 123 are provided on the uppersurface of the camera body 111. The release button 121 is associatedwith a photometering switch SWS and a release switch SWR, so that whenthe release button 121 is half-depressed, the Photometering switch SWSis turned ON and when the release button 121 is fully depressed, therelease switch SWR is turned ON, respectively.

A zoom lever 125 is provided on the upper portion of the back surface ofthe camera body 111. When the zoom lever 125 is moved toward a telephotoside or a wide-angle side, the zoom lens 113 is respectively moved inthe telephoto direction or the wide-angle direction to perform thezooming operation. The zoom lever 125 is associated with a telephotoswitch SWTELE and a wide-angle switch SWWIDE, so that when the zoomlever 125 is moved toward the telephoto side or the wide-angle side, thetelephoto switch SWTELE or the wide-angle switch SWWIDE is respectivelyturned ON.

A self-timer light emitter 127 is also provided on the front surface ofthe camera body 111. The light emitter 127 is adapted not only toindicate that the self-timer is in operation, but also serves as areleasing operation notifying light emitter. Also, a green light emitter128 and a red light emitter 129 are provided in the vicinity of aviewfinder provided on the back surface of the camera body 111. Thegreen light emitter 128 indicates whether a subject is in-focus or not,while the red light emitter 129 indicates whether a strobe light isavailable or not.

FIG. 37 shows a block diagram of a circuit of the lens-shutter typecamera shown in FIGS. 35 and 36. A CPU 131 is provided in the camerabody 111 and generally controls various photographing operations, suchas, an automatic focus control (AF control), an automatic exposurecontrol (AE control), film winding and rewinding operations, etc. Thephotometering switch SWS, the release switch SWR, the telephoto switchSWTELE and the wide-angle switch SWWIDE, are all connected to the CPU131. The CPU 131 performs predetermined operations in response to theON/OFF state of the above switches.

A DX-code reading circuit 133 reads a DX-code printed on a film patrone,corresponding to ISO speed values, through DX-code contact pins (notshown) and outputs the signals read to the CPU 131. A zoom code inputcircuit 135 detects the current focal length data of the zoom lens 113through a zoom code plate (not shown) and supplies the detected signalsto the CPU 131.

A photometering circuit 137 is provided with a photometering sensor (notshown) which receives subject light incident thereupon through thephotometering window 115 and converts the optical signals intophotometering signals having an electric current voltage, correspondingto the subject brightness, to supply the same to the CPU 131. The CPU131 calculates subject brightness (brightness value) Bv in accordancewith the photometering signal to obtain an optimum shutter speed (timevalue) Tv and an optimum aperture value Av in accordance with thesubject brightness Bv and the ISO speed value Sv that has been readthrough and converted by the DX-code reading circuit 113.

The AF auxiliary light emitting circuit 139 actuates an AF auxiliarylight emitter (not shown) to illuminate a subject with light having acontrasting pattern, under the control of the CPU 131 when the CPU 131judges that the subject brightness Bv is low or subject contrast is low.

The distance measuring unit 151 which also functions as a subjectdistance detecting means, receives light reflected from the subject andproduces and outputs a pair of two dimensional image signals, eachincluding several image signals. The image signals are stored in aninternal RAM for each image signal unit. The CPU 131 calculates asubject distance in accordance with the pair of image signals stored inthe RAM to thereby obtain a displacement of the focusing lens. Thefocusing lens is driven to a point corresponding to the displacementthus obtained, by an exposure/focus drive circuit 141. A strobe drivingcircuit 143 actuates the strobe light emitter 119. A finder LCD 147connected to the CPU 131 and provided in the viewfinder of the camera ofthis embodiment indicates an AF frame, and various photographinginformation, etc.

In the camera, the shutter and aperture are driven by the exposure/focusdrive circuit 141 in accordance with the shutter speed Tv and theaperture value Av determined by the CPU 131 when the release switch SWRis turned ON.

When the telephoto switch SWTELE or the wide-angle switch SWWIDE areturned ON, the CPU 131 drives a zoom motor M through a zoom motor drivecircuit 145 to move the zoom lens 113 towards a respective telephoto orwide-angle extremity. When the main switch of the camera is turned OFF,the zoom motor M moves the lens barrel of the zoom lens 113 to itsaccomodated position or retracted position, in which the lens barrel iscompletely retracted into the camera body 111. When the main switch isturned ON, the lens barrel is moved to the wide-angle extremity by thezoom motor M.

The zoom lens 113 has a macro photography function, so that when a macroswitch (not shown) is turned ON, the zoom motor M is driven to move thezoom lens 113 to a macro position beyond the telephoto extremity.

The self-timer light emitter 127, the green light emitter 128 and thered light emitter 129, are driven by a light emitter driving circuit149. A finder LCD 147 is provided in the finder to indicate variousphotographing information in the finder view.

In addition to the main components of the camera as mentioned above, thecamera is also provided with a battery, an indication panel in whichvarious photographing information is indicated, and a film winding andrewinding motor, etc.

FIG. 38 shows a block diagram of the distance measuring unit 151, whichis comprised of a pair of left and right image forming lenses (condenserlenses) 152L and 152R, a pair of left and right line sensors 153L and153R, a pair of left and right quantizing portions 154L and 154R, and acontroller 155. It should be noted that both the left and right halvesof the above are identical and operate in the same fashion.

Subject light received is converged on, or in the vicinity, of the linesensors 153L and 153R by the corresponding image forming lenses 152L and152R. Photodiodes (light receiving elements) of the line sensors 153Land 153R, that receive the subject light, produce electric signalscorresponding to the brightness of the light received, and output thesame to the quantizing portions 154L and 154R, respectively. Thequantizing portions 154L and 154R integrate the quantity of the lightreceived by the photodiodes (electric signals input thereto) and detectthe time at which the integral value has reached a constant value. Thedetected time is stored. The detected time data reduces as subject imagebrightness increases.

When all the times are detected and stored as a result of the integraloperation of the electric signals by the quantizing portions 154L and154R, or when a predetermined time elapses before the integral valuebecomes a predetermined value, the predetermined time is stored as ameasurement time for the photodiode in which the integral operation hasnot completed. Consequently, the memorized measurement time data issuccessively output to the CPU 131 as image data through a controller155. The CPU 131 then stores the image data. The measurement time data,i.e., the image data, becomes a small value as the subject imagebrightness increases.

More specifically, a comparator and a latch circuit, included in thecorresponding quantizing portion 154L or 154R, are connected to eachlight receiving element, and the electric charge accumulated in eachlight receiving element is quantized through the correspondingcomparator and latch circuit. The quantized data of each line sensor153L, 153R is sent to the CPU 131 in serial order through the controller155. Amongst all the sensor data obtained from all of the lightreceiving elements on each line sensor 153L, 153R, the CPU 131 can onlyselect a part of all the sensor data correspondingly from each linesensor 153L, 153R and use only this selected sensor data for a distancemeasuring operation.

Note that the image data of the photodiodes of the line sensors 153L and153R will also be referred to as "bit data".

FIGS. 40 and 41 show a relationship between the light receiving areasused for a multiple measurement and the line sensors. According to thecamera of the fifth aspect of the present invention there are five lightreceiving areas, namely, a central light receiving area MC, left andright light receiving areas ML and MR on the left and right sides of thecentral light receiving area MC, and left and right intermediate lightreceiving areas MLC and MRC provided between the central light receivingarea MC and the left and right light receiving areas ML and MR,respectively. Light receiving areas MC, ML, MR, MLC and MRC of the linesensors 153L and 153R correspond to respective subject light receivableranges mc, ml, mr, mlc and mrc. The line sensors 153L and 153R are eachprovided with 128 photodiodes which serve as light receiving means. Eachlight receiving area contains 36 consecutive photodiodes.

FIG. 39 shows the principle of measurement by the distance measuringunit 151. In FIG. 39, "f" presents the focal length of the image forminglenses 152L and 152R. "OA₁ " and "OA₂ " represent the optical axes ofthe image forming lenses 152L and 152R, respectively, which are disposedparallel to each other and apart from each other by a distance "B". "b₁" and "b₂ " represent the points of incidence of the optical axes OA₁and OA₂ upon the line sensors 153L and 153R, respectively. Accordingly,the distance between the incident points b₁ and b₂ is the base lengthwhich is equal to the distance B. "P" represents a subject and "Lx"represents the distance from the subject P to the pair of image forminglenses 152L and 152R. Here, for the purpose of illustration, the subjectP is regarded as a mere point having no length or width. It is assumedthat images of a subject P, located at the subject distance Lx, arerespectively formed at the points X₁ and X₂ on the line sensors 153L and153R by the respective image forming lenses 152L and 152R, and that thedistance between the image points X₁ and X₂ is x. It is also assumedthat the distance between the points b1 and X₁ is XL, and the distancebetween the points b2 and X₂ is XR. Accordingly, the following relationcan be obtained:

    B:(XL+XR)=Lx:f

The subject distance Lx is given by:

    Lx=Bxf/(XL+XR)=Bxf/(x-B)

In the illustrated embodiment, the focal length f of the image forminglenses 152L and 152R and the distance therebetween, i.e., the baselength B, are fixed values. Consequently, the subject distance Lx can beobtained by calculating the distances XL and XR or the distance x. Inthis embodiment, the image points X₁ and X₂ are detected to obtain thedistance x to obtain the subject distance Lx.

In general, a subject to be photographed is not merely a point and hencethe subject images to be formed on the line sensors 153L and 153R aretwo dimensional. Therefore, the image points X₁ and X₂ cannot bedirectly detected.

To solve this, a predetermined number of light receiving elements (e.g.,1 or 2 elements) of the line sensor 153L are compared with the samenumber of light receiving elements of the line sensor 153R. Thiscomparison is repeatedly carried out while relatively changing the lightreceiving elements to be compared. When the highest degree ofcoincidence of the distribution of the quantity of light defined by thelight receiving elements between the line sensors 152L and 153R isobtained, the distance between the light receiving elements isdetermined to be the image distance x.

The synopsis of the calculation of the Subject distance will beexplained below referring to FIG. 42. The addresses of the photodiodesof the left line sensor 153L are L(NL) and the addresses of thephotodiodes of the right sensor 153R are R(NR). Assuming that the lightreceiving areas (image data) to be used for the calculation of thesubject distance are selected as shown in FIG. 42, the evaluationfunction f(N) which represents the degree of coincidence of the imagedata between the line sensors 153L and 153R is given by the followingformula 1: ##EQU1## wherein

    N2=N1 or N2=N1+1, and

    0≦N1+N2≦24

In this embodiment, WO is 24, wherein WO stands for the number of bitsused in the light receiving area. The correlative evaluation dataobtained by the evaluation function f(N) decreases as the degree ofcoincidence of the image data increases. When the degree of coincidenceis highest, the minimum value of the evaluation function f(N) isobtained. The minimum value is given by the following formula:

    f(N-1)≦f(N)<f(N+1)

Note, when the left and right image data groups are identical, theevaluation function is zero, i.e., f(N)=0. As can be understood from theforegoing, the minimum value of the evaluation function f(N) is obtainedby calculating the evaluation function f(N) wherein the light receivingareas to be compared are relatively switched or shifted by onephotodiode at each comparison. In general, when the minimum value isobtained, the degree of coincidence becomes highest. The position atwhich the degree of coincidence becomes highest is determined from areference position (sensor start address) of each light receiving area.

FIGS. 43 through 45 show graphs of exemplary image data detected by thedistance measuring unit 151, the image data of the light receiving areasto be used for the calculation of the subject distance and theevaluation function f(N). In these drawings, the ordinate represents thebrightness and the abscissa represents the position of the lightreceiving areas of the line sensors 153L and 153R. In FIGS. 43 through45, (A) designates the image data of all of the light receiving areas ofthe line sensors 153L and 153R, (B) the image data of the selected lightreceiving areas of the line sensors 153L and 153R, (C) the correlativeevaluation data, (L) the data on the left line sensor 153L and (R) thedata on the right line sensor 153R. Note that in the bar graphs, thebrightness increases as the height of the bars or lines decreases. Also,the degree of coincidence becomes high as the height of the bars orlines decreases.

As can be seen in FIG. 43, when there is no difference in the quantityof light to be received by the line sensors 153L and 153R, the minimumvalue at which the value of the evaluation function f(N) isapproximately zero can be obtained. However, as shown in FIG. 44, whenthere is a difference in the quantity of light between the line sensors153L and 153R, the minimum value of the evaluation function f(N) isidentical to the difference in the quantity of light, and hence themeasurement might be judged to be an error.

In the fifth aspect of the invention, even in such a case, an error inthe judgement of the measurement does not occur. To this end, as shownin FIG. 45, in the fifth embodiment, the minimum values (brightest imagedata) among the respective image data obtained from the line sensors153L and 153R are extracted to obtain a difference therebetween.Thereafter, the difference is subtracted from the respective image dataof the brighter light receiving areas to correct the image data, asshown in FIG. 45B. Consequently, the level of the image data is shiftedwhile maintaining the wave shape of the distribution pattern of thequantity of light. The correlative evaluation data at which the peakvalue is approximately zero can be obtained by calculating theevaluation function f(N) in accordance with the corrected image data.

The operation of the camera mentioned above will be discussed below withreference to the flow charts shown in FIGS. 46 through 56. The operationis carried out by the CPU 131 in accordance with a program stored in theinternal ROM of the CPU 131.

When the main switch of the camera is turned ON, the control begins theoperation shown in the flow chart of FIG. 46. First, the ON/OFF state ofthe switches SW is input to the CPU (Step S1101). Thereafter, whether ornot the telephoto switch SWTELE and the wide-angle switch SWWIDE areturned ON is checked at Steps S1103, S1113, respectively. If thetelephoto switch SWTELE is turned ON, it is then checked whether thezoom lens is at the telephoto extremity (Step S1105). If the zoom lensis at the telephoto extremity, control proceeds to Step S1113. If thezoom lens is not at the telephoto extremity, nor at the macro position(Step S1107), the zoom lens is moved in the telephoto direction by thezoom motor M (Step S1109). Thereafter, the control is returned to StepS1101. If the zoom lens is located at the macro position (Step S1107),the zoom lens 113 is moved to the telephoto extremity (Step S1111).Thereafter, the control is returned to Step S1101.

Note that in the course of the zooming operation in the telephotodirection, the zoom motor M is driven to move the zoom lens 113 towardsthe telephoto extremity while the telephoto switch SWTELE is ON. If thezoom switch SW is turned OFF or the zoom lens 113 reaches the telephotoextremity, the zoom motor M is stopped. Thereafter, the control isreturned to Step S1101.

If the wide-angle switch SWWIDE is turned ON (Step S1113), it is thenchecked if the zoom lens is at the wide-angle extremity (Step S1115). Ifthe zoom lens is at the wide-angle extremity control proceeds to StepS1123, but if the zoom lens 113 is not at the wide-angle extremity (StepS1115), nor at the macro position (Step S1117), the zooming operation inthe wide-angle direction is carried out (Step S1119). Thereafter, thecontrol is returned to Step S1101. If the zoom lens is at the macroposition (Step S1117), the zoom lens is moved to the telephoto extremityand the control is returned to Step S1101 (Step S1121).

At Step S1123 it is checked if the photometering switch SWS is switchedfrom OFF to ON. If the photometering switch SWS is ON, control proceedsto a "Photographing Operation" subroutine at Step S1125. Conversely, ifthe photometering switch SWS is OFF, the control is returned to StepS1101. When the "Photographing Operation" subroutine is complete controlreturns to Step S1101.

The "Photographing Operation" subroutine will be discussed below withreference to the flow charts shown in FIGS. 47 and 48.

When the control enters this subroutine, the DX-code reading circuit 133is driven to input the ISO speed information (Step S1201), andthereafter the remaining battery voltage is checked (Step S1203). If thebattery voltage is below a predetermined value, the control is returnedbecause there is a possibility that normal photographing operations cannot be executed. Namely, the real photographing operation starts whenthe battery voltage is above a predetermined value (Step S1205).

If the battery voltage is above a predetermined value, the distancemeasuring unit 151 is driven and the distance data is input to obtainthe subject distance (Step S1207). The subject distance is obtained in a"Subject Distance Measuring Operation" subroutine, shown in FIG. 49.Thereafter, the photometering circuit 137 is driven to input thephotometering data to thereby obtain the subject brightness, whereby theshutter speed Tv and the aperture value Av can be calculated inaccordance with a predetermined "AE Calculating Operation" (Step S1209,Step S1211). Thereafter, whether or not the subject distance data has adefault is checked (Step S1213). The subject distance data has adefault, i.e., the measurement data is in error, for example when thesubject contrast is too low to obtain the defocus amount. In case of ameasurement error, the green light emitter 128 is blinked to indicatethe measurement error (Steps S1215, S1221). Even if the measurement isnot in error, if the subject distance is shorter than the shortestsubject distance the green lighter emitter 128 is blinked (Steps S1215,S1217, S1221). If the measurement is neither in error nor the subjectdistance is shorter than the shortest subject distance, the green lightemitter 128 is lit (Steps S1215, S1217, S1219).

After that, whether the strobe light should be emitted is checked (StepS1223). If the strobe light is to be emitted, an FM (flashmatic)operation is carried out to obtain the aperture value Av (Step S1225).When the FM operation has completed, whether or not the strobe charginghas completed is checked (Step S1227). If the charging has completed,the red light emitter 129 is lit (Step S1229), while if charging has notcompleted, the red light emitter 129 is blinked (Step S1231).

Thereafter, the states of the photometering switch SWS and releaseswitch SWR are input (Step S1233). No operation starts until the releaseswitch SWR is turned ON (Steps S1235, S1237). If the photometeringswitch SWS is turned OFF before the release switch SWR is turned ON,both the green light emitter 128 and the red light emitter 129 areextinguished, and the control is returned (Steps S1237, S1239).

If the release switch SWR is turned ON (Step S1235), the self-timerlight emitter 127 is lit to notify that a shutter will soon be releasedand the green light emitter 128 and the red light emitter 129 areextinguished (Step S1241). After that, the focusing lens is driven (Step1243) and the self-timer light emitter 127 is extinguished (Step S1245)to perform the exposure operation (Step S1247) and the filmwinding/rewinding operation (Step S1249). After that, the control isreturned to the main routine.

FIG. 49 shows the "Subject Distance Measuring Operation" subroutine atStep S1207. In this subroutine, various data, including thephotometering value, on the subject distance is read from the ROM andRAM (Step S1301). Thereafter, whether the photometer value is above apredetermined emission level at which the auxiliary light should beemitted is checked (Step S1303). If the value is above the predeterminedemission level, the AF auxiliary light emitting circuit 139 is turnedOFF (Step S1305). Conversely, if the value is below the predeterminedemission level, the AF auxiliary light emitting circuit 139 is activatedto commence the emission of the auxiliary light (Step S1307).

The integral completion time is set (Step S1309), and the variable "i",which determines the number of the measuring operations, is set "0"(Step S1311). Thereafter (FIG. 50), the distance measuring unit 151 isreset, i.e., the integral values are swept to start the integraloperation of the distance measuring unit 151 (Step S1313). In thisembodiment, the distance measuring unit 151 to which the reset signal issupplied from the CPU 131 executes the integral operation. Consequently,the data for each photodiode of the line sensors 153L and 153R issupplied to the CPU 131 which stores the data bits in the RAM.

After the distance measuring unit 151 is reset (Step S1313), the lightreceiving areas to be used for the calculation of the subject distanceare set (Step S1315). Namely, the right line sensor starting address NRand the left line sensor starting address NL are set to commence thereading operation of the image data (Steps S1401, S1403 in FIG. 51). Apredetermined number of the image data determined from the addresses ofthe set light receiving areas are read to perform a "Data CorrectingOperation" subroutine (FIG. 52), in which the levels of the image dataof the right and left line sensors are made identical (Steps S1317,S1319).

Thereafter, at Step S1321, a subroutine "Interpolation ArithmeticOperation" shown in FIG. 55 is carried out so as to obtain, for eachline sensor 153L, 153R, the Position (i.e., the center position) of asubject image formed on a corresponding line sensor. The subroutine"Interpolation Calculation Operation" of the evaluation function f(N) isincluded in the subroutine "Interpolation Arithmetic Operation".

The above-mentioned operations at Steps S1315 through S1321 are effectedfor each of the five light receiving areas MC, ML, MR, MLC and MRC(Steps S1323, S1315 to S1323).

Upon completion of the subroutine "Interpolation Arithmetic Operation"for each light receiving area, a subject image distance value iscalculated for each of all the light receiving areas MC, ML, MR, MLC,based on triangulation as explained above with reference to FIG. 39, tothereby obtain five subject image distance values, and subsequently, oneof the five subject image distance values is selected, at a subroutinelabelled "Subject Image Distance Value Calculating and SelectingOperation", at Step S1325. Note that "subject image distance value" is avalue corresponding to the distance of "x-B" (i.e., the distance "x"minus the distance "B") shown in FIG. 39. Therefore, the greater thesubject image distance value is, the closer a subject to be photographedis to the camera.

If no correct subject image distance value is obtained, i.e., if all thesubject image distance values are in error when the subroutine "SubjectImage Distance Value Calculating and Selecting Operation" at Step S1325is completed, the auxiliary light is emitted once by the AF auxiliarylight emitter (not shown), actuated by the AF auxiliary light emittingcircuit 139, to again carry out the operations at Steps S1313 throughS1325 (Steps S1327, S1329, S1331, S1333 and S1313 through S1325).

If a correct or effective subject image distance value is obtained fromat least one light receiving area from the operations at Steps S1313through S1325, or if the operations at Steps S1313 through S1325 havecompleted for a second time, it is then checked at Step S1335 whether ornot the subject image distance values for all the light receiving areasare in error. If all the values are not in error, i.e., if at least onecorrect subject image distance value is obtained, that subject imagedistance value is converted into displacement data (LL) for the focusinglens at Step S1337. Thereafter, the control returns. If it is judgedthat all the subject image distance values are in error at Step S1335, ameasurement error flag is set at Step S1339 and the control returns.

The subroutine "Subject Distance Measuring Operation" will now bedescribed below in more detail with reference to FIGS. 52 through 56.

FIG. 52 shows the "Data Correcting Operation" subroutine at Step S1319.When the control enters this subroutine, the minimum value Lmin of theimage data (left sensor data) of the left line sensor 153L correspondingto the maximum subject brightness, and the minimum value Rmin of theimage data (right sensor data) of the right line sensor 153Rcorresponding to the maximum subject brightness are detected (StepS1501). Thereafter, a difference D, between the minimum values Lmin andRmin is calculated (Step S1503). If the difference D is larger than 0,i.e , if the minimum value Lmin is larger than the minimum value Rmin,the left line sensor data is corrected (Steps S1505, S1507). If thedifference D is smaller than 0, i.e., if the minimum value Rmin islarger than the minimum value Lmin, the right line sensor data iscorrected (Steps S1505, S1509, S1511). If the difference D is 0, i.e.,if the minimum value Lmin is identical to the minimum value Rmin, thecontrol is returned (Steps S1505, S1509) Namely, the data correction iseffected in accordance with a comparison of image data at the brightestpoints on the left and right line sensors.

The "Sensor Correcting Operation" subroutine at Steps S1507 and S1511will be described below with reference to FIGS. 53 and 54.

In this subroutine, the difference D is added to one of the left orright sensor data whose minimum value is smaller than that of the othersensor data, to make the data levels of the left and right sensor dataidentical. Upon correction of the left sensor data, the variable "i" isset zero (Step S521). Thereafter, the image data L (NL+i) at the addressof (NL+i) is substituted by a value which is obtained by subtracting thedifference |D| (absolute value) from the image data L(NL+i) at StepS523, and then, 1 is added to the variable "i" (Step S525). Theoperations mentioned above are repeated until the variable "i" becomesmore than WO (i.e., 24)+12 (Step S527).

Similarly, in the correction of the right sensor data, the variable "i"is set zero (Step S531). Thereafter, the image data R(NR+i) at theaddress of (NR+i) is substituted by a value which is obtained bysubtracting the difference |D| (absolute value) from the image dataR(NR+i) at Step S533, and then, 1 is added to the variable "i" (StepS535). The operations mentioned above are repeated until the variable"i" becomes more than WO+12 at Step S537.

As a result of the correction of the left and right sensor data, thedifference D therebetween can be subtracted from each piece of imagedata corresponding to each measuring area to correct the image data.

The "Interpolation Arithmetic Operation" subroutine at Step S1321 willbe discussed below with reference to FIG. 55.

In this subroutine, the variable N1 is set at zero (Step S601).Thereafter, the variable N1 is replaced by the variable N2, and the sumof the variables N1 and N2 is replaced by variable N (Step S603) tocalculate the evaluation function f(N) at Step S605. Thereafter, thevariable N2 is set to equal (N1+1) and the variable N is set to equal(N1+N2), to calculate the evaluation function f(N) at Steps S607 andS609. When the calculation of the evaluation function f(N) hascompleted, the variable N1 is set to equal (N1+1) at Step S611.

The operations at Steps S603 through S611 are repeated until thevariable N becomes 25. Namely, each operation is repeated by shiftingthe bit one at a time (Steps S613, S603 through S611).

When twenty five values of the evaluation function f(N) are obtained,the minimum value, i.e., light receiving area corresponding to thehighest degree of coincidence of the distribution patterns of thequantity of light, is selected from among the twenty five values (StepS615) Thereafter, whether or not there are a plurality of minimum values(i.e., whether the measurement is defective) is checked. If themeasurement is not defective, the "Interpolation Calculation Operation"is carried out and the control is returned (Steps S617, S619, S621). Ifthe measurement is defective, the error bit is set and the control isreturned (Steps S617, S619, S623). If the error bit is set, themeasurement error operations, such as blinking the green light emitter28 or a locking of the release, etc., are carried out.

The "Evaluation Function f(N) Operation" subroutine at Steps S605 andS609 will be discussed below with reference to FIG. 56.

In the calculation of the evaluation function f(N), the sum of thedifferences between the corresponding bit data of the right and leftlight receiving areas is obtained for each bit of the light receivingarea.

The variable "i" and the evaluation function f(N) are both set zero(Step S631). Thereafter, the values of the evaluation function f(N) arecalculated by increasing the value of the variable "i" one by one fromzero to WO (Steps S633, S635 and S637). Consequently, data of theevaluation function f(N) is obtained.

In the illustrated embodiment, the right and left light receiving areasare alternately shifted one bit by one bit by the operation shown inFIG. 55. The shifting operations for 12 bits in total take place toobtain twenty five values of the evaluation function f(N). The number ofbits to be shifted in one operation and the total number of bits are notlimited to those in the illustrated embodiment.

As can be seen from the above discussion, according to the fifth aspectof the present invention, if there is a difference in the quantity oflight between the left and right line sensors 153L and 153R, the imagedata of one of the line sensors is entirely corrected without modifyingthe wave shape defined by the image data. Thus, even if there is aremarkable difference in the quantity of light between the left andright line sensors, a correct subject image distance value can beobtained.

As may be understood from the foregoing, according to the fifth aspectof the present invention in which the distance measuring apparatusincludes a pair of line sensors, image data corresponding to the maximumbrightness (maximum brightness equivalent values) in each line sensor isdetected from among the image data supplied from the light receivingareas of the line sensors. Thereafter, the difference between themaximum brightness equivalent values is obtained. Consequently, theimage data of one of the line sensors is corrected in accordance withthe difference data. Therefore, even if there is a considerabledifference in the quantity of light received by the line sensors, thedifference can be absorbed or cancelled, and hence, a precise automaticfocusing operation can be achieved.

Another embodiment (i.e., a sixth embodiment) of a camera to which adistance measuring apparatus according to a sixth aspect of the presentinvention is applied will be discussed below. The camera of the sixthembodiment is similar to the camera of the fifth embodiment to which thefifth aspect of the present invention is applied, except in severalrespects. The following explanation will only be directed to thatstructure unique to the sixth embodiment. The camera of the sixthembodiment will be explained below with reference to FIGS. 35˜42, 46˜49,51˜54, 56, and 57˜63.

Although the minimum value of the evaluation function can be obtained byusing the aforementioned evaluation function f(N) at each photodiode(light receiving element) of each line sensor, sometimes the realminimum value exists between two photodiodes (i.e., between the centerof one photodiode and the center of an adjacent photodiode). FIG. 57shows the principle of calculating the minimum value of the evaluationfunction with the aforementioned evaluation function f(N) byinterpolation.

In this interpolative calculation, a section between two photodiodes, inwhich the real minimum value is considered to exist, is firstly found,and subsequently, two straight lines which intersect in the sectionfound are set. Then, the coordinate point of the intersection of the twostraight lines is calculated. In the case shown in FIG. 57, thecoordinates (x,y) of the intersection I of the two straight lines iscalculated by two straight lines respectively passing through two pairsof points, ire., the first pair (x₀, y₀) and (x₁, y₁) and the secondpair (x₂, y₂) and (x₃, y₃), between which the real minimum value isconsidered to exist. In FIG. 57, the X-coordinate and the Y-coordinaterepresent the center of a subject image formed on a light receiving areaof a line sensor and the evaluation value, respectively. TheX-coordinate of the intersection I "x" represents the center of aspecific subject image formed on a light receiving area.

It will be appreciated from FIG. 57 that the steeper the two straightlines are, the more precisely the position of the center "x" can bedetected. Namely, the higher the contrast of a subject is, the steeperthe two straight lines become and thus the position of the center "x"can be detected more precisely. The lower the contrast of a subject is,the flatter the two straight lines become and thus the detection of theposition of the center "x" becomes more imprecise.

Furthermore, in the case where a subject image having a repetitivepattern exists within a light receiving area or in the case where imagesof near distance subjects and far distance subjects coexist within thelight receiving area, more than one minimum value of the evaluationfunction exists. In such a case, it is impossible to precisely judgewhich minimum value is the real minimum value.

To solve this problem, according to the distance measuring apparatus towhich the sixth aspect of the present invention is applied, theprecision of subject distance measuring can be made higher, when thecontrast of an image of a subject to be photographed is low, byenlarging the light receiving area in which the contrast is low, in bothof the line sensors, i.e., if image contrast is low in MC, for example,MC is enlarged. Similarly, when images of near distance subjects and fardistance subjects coexist within a light receiving area, that particularmeasuring area is narrowed.

FIGS. 58 and 59 show graphs of the image data detected by the distancemeasuring unit 151, the image data of the light receiving areas to beused for the calculation of the subject image distance value and theevaluation function f(N), by way of example. In these drawings, theordinate represents the brightness and the abscissa represents theposition of the light receiving areas of the line sensors 153L and 153R.In FIGS. 58 and 59, (a) and (A) each designate the image data of all ofthe light receiving areas of the line sensors 153L and 153R, (b) and (B)the image data of the selected light receiving areas of the line sensors153L and 153R, (c) and (C) the correlative evaluation data, "L" the dataon the left line sensor 153L and "R" the data on the right line sensor153R. Also in FIGS. 58 and 59, (a), (b) and (c) show the data of theprior art, while (A), (B) and (C) show the data of 10 the sixthembodiment of the present invention. Note that in the bar graphs, thebrightness increases as the height of the bars or lines decreases. Also,the degree of coincidence becomes high as the height of the bars orlines decreases.

FIG. 58 shows examples when the contrast within a regular lightreceiving area is low. In this case, specifically in the case of theprior art of (a), (b) and (c), the minimum value of the correlativeevaluation data cannot be accurately derived, thus leading to an errorin a subject image distance value measurement. To solve this problem, inthe sixth embodiment of the present invention, a light receiving area isenlarged when the contrast of a subject image within that particularlight receiving area is low. Thus, in the enlarged light receiving areathe chances of a subject image existing having a high contrast areincreased. Accordingly, the appropriate correlative evaluation data isobtained and the possibility of obtaining an accurate subject imagedistance value increases.

FIG. 59 shows examples when images of near distance subjects and fardistance subjects coexist within a regular light receiving area. In thiscase, specifically in the case of the prior art of (a), (b) and (c), theminimum value of the correlative evaluation data cannot be specifiedsince the correlative evaluation data includes a plurality of minimumvalues, thus leading to an error in a subject image distance valuemeasurement. To solve this problem, in the sixth embodiment of thepresent invention, a light receiving area, in which images of neardistance subjects and far distance subjects coexist, is narrowed thusreducing the number of subject images coexisting within that particularlight receiving area. In other words, a subject image coexisting withanother subject image within a regular light receiving area is notincluded in the narrowed light receiving area. Thus, the precision ofsubject image distance value measuring can be increased.

Note that in the camera of the sixth embodiment to which the sixthaspect of the present invention is applied, a default occurring becausea subject image has a low contrast, is defined as "1", and that adefault occurring due to an existence of a plurality of minimum valuesin the correlative evaluation data, even when a subject to bephotographed has a high contrast, is defined as "2", so as todistinguish the former type of default from the latter type. Note thatthe subject image could also have a low contrast due to either a darksubject or a blurry subject image (due to a subject being out of focus,for example).

The operation of the camera of the sixth embodiment having the abovementioned circuit structure will be hereinafter discussed. The mainroutine performed by the CPU 131 is the same as that of the camera ofthe fifth embodiment which is shown in FIG. 46.

The subroutine "Photographing Operation" at Step S1125 in the mainroutine is also the same as that in the camera of the fifth embodimentwhich is shown in FIGS. 47 and 48.

The subroutine "Subject Distance Measuring Operation" at Step S1207 inthe camera of the sixth embodiment will be discussed below withreference to FIGS. 49, 50 and 60.

The subroutine "Subject Distance Measuring Operation" in the camera ofthe sixth embodiment is identical to that of the camera of the fifthembodiment (shown in FIGS. 49 and 50), except that the former subroutineincludes the operations at Steps S1350, S1352 and S1354 between StepsS1321 and S1323 whereas the latter subroutine does not include the samebetween Steps S1321 and S1323 (FIG. 50). The following explanation ofthe subroutine "Subject Distance Measuring Operation" in the camera ofsixth embodiment, will only be directed to those steps unique to thesixth embodiment, i.e., Steps S1350, S1352 and S1354.

After passing through the subroutine "Interpolation ArithmeticOperation" at Step S1321, the control proceeds to Step S1350 to check ifthe measuring data calculated in the subroutine "InterpolationArithmetic Operation" at Step S1321 has a default or not, i.e., if thedefault is "0" or not. If it is judged that the default is not "0" atStep S1350, i.e., the default is "1" or "2", the control proceeds to asubroutine labelled "Measuring Area Resetting Operation" at Step S1352.Here the corresponding light receiving area having the default "1" or"2" is enlarged or narrowed.

After Step S1352 the control proceeds to a subroutine labelled"Interpolation Arithmetic Operation" at Step S1354, similar to thesubroutine at Step S1321, to again carry out an interpolation arithmeticoperation, and thereafter, the control proceeds to Step S1323. Hence,the operations at Steps S1315 through S1321 and Steps S1350 throughS1354 are effected for each of the five light receiving areas MC, ML,MR, MLC and MRC (Steps S1323, S1315 to S1321, S1350 to S1354, andS1323).

The subroutine "Interpolation Arithmetic Operation" at Step S1321 orS1354 will be hereinafter discussed with reference to a flow chart shownin FIG. 61. The subroutine shown in FIG. 61 is the same as that in thecamera of the fifth embodiment which is shown in FIG. 55, except thatthe subroutine "Interpolation Arithmetic Operation" of the sixthembodiment has an operation at Step S602 immediately after Step S601,and it does not have operations corresponding to Steps S619, S621 andS623, but instead has operations at Steps S625 and S627. The followingexplanation of the subroutine "Interpolation Arithmetic Operation" willonly be directed to those steps unique to the sixth embodiment, i.e.,Steps S602, S625 and S627.

After the operation of Step S601, the control proceeds to a subroutinelabelled "Maximum and Minimum Values Detecting Operation" at Step S602.Here a maximum value and a minimum value in the bit data are detectedfor each line sensor 153L, 153R, and subsequently, the control proceedsto Step S603.

After the subroutine "Default Check Operation" at Step S617, the controlproceeds to Step S625 to check whether the default is "0" or not. If itis judged at Step S625 that the default is "0", the control proceeds toa subroutine labelled "Interpolative Calculating Operation" at StepS627. If it is judged at Step S625 that the default is not "0", thecontrol returns.

In the camera of the sixth embodiment, the subroutines "Measuring AreaSetting Operation" at Step S1315 and "Data Correcting Operation" at StepS1319 are the same as those in the camera of the fifth embodiment whichare shown in FIGS. 51 and 52, respectively. Furthermore, the subroutines"Sensor Correcting Operation" in the subroutine "Data CorrectingOperation" at Step S1319 are also the same as those in the camera of thefifth embodiment which are shown in FIGS. 53 and 54, respectively.

The subroutine "Default Check Operation" at Step S617 will behereinafter discussed with reference to a flowchart shown in FIG. 62. Inthis subroutine it is checked if the contrast of a subject image is low,and if images of near distance subjects and far distance subjectscoexist in the light receiving area when judging that the contrast of asubject image is not low.

When the control enters this subroutine, the default is set as "0" atStep S651 Thereafter, at Step S653, maximum and minimum value bit datafor each line sensor 153L and 153P, which have been detected at StepS602, are stored in an internal RAM, and the difference between themaximum value and the minimum value is calculated for each of the linesensors 153L and 153R as the difference DL and the difference DR,respectively.

Thereafter, at Step S655 each difference DL, DR is checked as to whetheror not it is greater than a predetermined value, e.g., 12. If thedifferences DL, DR are both equal to or smaller than the predeterminedvalue, the control proceeds to Step S657 where the default is set "1".Here it is judged that the contrast is too low.

If it is judged that at least one of the differences DL, DR is greaterthan the predetermined value at Step S655, the control proceeds to StepS659 to check if the number of the minimum value of the correlativeevaluation data is one or more than one. The control returns if thenumber is one, and it is judged that the correlative evaluation data isan appropriate data, or proceeds to Step S661 if the number is more thanone, i.e., a series of minimum values of the correlative evaluation dataexist.

At Step S661 the lowest minimum value and the second lowest minimumvalue of the correlative evaluation data are defined as "K1" and "K2",respectively, and thereafter, at Step S663, the difference between K1and K2 is calculated. If the difference is equal to or greater than apredetermined value, e.g., 50, the control returns with an assumptionthat an effective subject image distance value measuring data has beenobtained. Conversely, if the difference is less than the predeterminedvalue, the control proceeds to Step S665 where the default is set "2"since subject images of near distance subjects and far distance subjectspossibly coexist in that light receiving area, and subsequently, thecontrol returns.

It will be accordingly appreciated that to correspond to each lightreceiving area MC, MR, ML, MRC and MLC, the default is set "0" when aproper subject image distance value is obtained at a light receivingarea, is set "1" when the contrast of a subject image is too low at alight receiving area, and is set "2" when images of near distancesubjects and far distance subjects coexist in a light receiving area.

Next, the subroutine "Measuring Area Resetting Operation" at Step S1352will be hereinafter discussed with reference to a flow chart shown inFIG. 63. In this subroutine, each light receiving area MC, MR, ML, MIRCor MLC is respectively enlarged or narrowed when the contrast of asubject image is low or not low at a light receiving area.

When the control enters this subroutine, it is checked at Step S701whether the default is "1" or "2". The control proceeds to Step S703 ifthe default is "1", or to Step S705 if the default is "2". At Step S703a predetermined number "a" is added to the number "WO" (i.e., the numberof bits used in a measuring area; "24" in this embodiment) so as toenlarge the corresponding light receiving area. At Step S705 apredetermined number "b" is subtracted from the number "WO" so as tonarrow the corresponding light receiving area.

As can be understood from the foregoing, according to the sixthembodiment of the present invention, when the subject image contrast islow, a light receiving area MC, MR, ML, MRC or MLC having a low contrastsubject image is enlarged, thereby the chances of obtaining a highcontrast subject image in that subject distance measuring area increase,as shown in FIG. 58(b) and (B) and also the chances of the correlativeevaluation data having a certain inclination (or steeper), as shown inFIG. 58(c) and (C), also increases. Thus, the possibility of performinga precise subject distance measuring when the subject image contrast islow increases.

On the other hand, in the case when a proper subject image distancevalue is not obtained, though the subject contrast is not low, withregular-size light receiving areas, i.e., when one subject imagedistance value, to be used for the focusing operation, cannot be decidedeven though the subject contrast is high enough with regular-size lightreceiving areas, it is assumed that images of near distance subjects andfar distance subjects coexist in a light receiving area. In this case,according to the sixth embodiment of the present invention, a lightreceiving area MC, MR, ML, MRC or MLC, which may have therein subjectimages of near distance subjects and far distance subjects, is narrowed,thereby decreasing the probability of having subject images of neardistance subjects and far distance subjects coexisting in a lightreceiving area, as shown in FIG. 59(b) and (B) and also the chances ofobtaining a single minimum value of the correlative evaluation dataincrease, as shown in FIG. 59(c) and (C). Thus, the possibility ofperforming precise subject distance measuring, even when a propersubject image distance value is not obtained though the subject contrastis not low with regular-size subject distance measuring areas,increases.

With the above structures of the sixth embodiment, even when a propersubject image distance value could not be obtained when the subjectdistance measuring calculation is firstly performed, the possibility ofobtaining a proper subject image distance value at a later subject imagedistance measuring calculation increases because of an expansion orreduction in the size of the light receiving area.

In the sixth embodiment of the present invention, it is preferable thatthe aforementioned predetermined numbers "a" and "b" are eachapproximately "10" (10 bits), but may be any other number.

Furthermore, in the sixth embodiment of the present invention, a lightreceiving area may be enlarged or narrowed step by step (by apredetermined number of bits) until a proper subject image distancevalue is obtained.

Still furthermore, in the sixth embodiment of the present invention,although a light receiving area is enlarged or narrowed in accordancewith the contrast of a subject image, a light receiving area may beenlarged or narrowed in accordance with the correlative evaluation data.In this case, a light receiving area is narrowed when the degree ofcorrelativity, between the subject image formed on one line sensor andthe subject image formed on the other line sensor, is low.

Another embodiment (i.e., a seventh embodiment) of a camera to which adistance measuring apparatus according to a seventh aspect of thepresent invention is applied will be discussed below. The camera of theseventh embodiment is similar to the camera of the fifth embodiment towhich the fifth aspect of the present invention is applied, except inseveral respects. Furthermore, some aspects of the camera of the seventhembodiment are the same as those of the camera of the sixth embodiment.For this reason, only those aspects unique to the camera of the seventhembodiment will be discussed below with reference to FIGS. 35˜43, 46 54,56, 57, 61, 62, 64 and 65.

Although the minimum value of the evaluation function can be obtained byusing the aforementioned evaluation function f(N) at each photodiode ofeach line sensor, sometimes the real minimum value exists between twophotodiodes (i.e., between the center of one photodiode and the centerof an adjacent photodiode). FIG. 57 shows the principle of calculatingthe minimum value of the evaluation function with the aforementionedevaluation function f(N) by interpolation.

In this interpolative calculation, a section between two photodiodes, inwhich the real minimum value is considered to exist, is firstly found,and subsequently, two straight lines which intersect in the sectionfound are set. Then, the coordinate point of the intersection of the twostraight lines is calculated. In the case shown in FIG. 57, thecoordinates (x,y) of the intersection I of the two straight lines iscalculated by two straight lines respectively passing through two pairsof points, i.e., the first pair (x₀, y₀) and (x₁, y₁) and the secondpair (X₂, y₂) and (x₃, y₃), between which the real minimum value isconsidered to exist. In FIG. 57, the X-coordinate and the Y-coordinaterepresent the image point and the evaluation value, respectively. TheX-coordinate "x" of the intersection I represents the image point of aspecific subject.

It will be appreciated from FIG. 57 that the steeper the two straightlines are, the more precisely the position of the center "x" can bedetected. In the camera of the seventh embodiment to which the seventhaspect of the present invention is applied, the degree of reliability ofa calculated subject image distance value is measured, based upon thedata of inclination of the above two straight lines, so as to judge ifthe calculated subject image distance value is effective or not.

The operation of the camera of the seventh embodiment will behereinafter discussed.

The main routine performed by the CPU 131 is the same as that of thecamera of the fifth embodiment which is shown in FIG. 46.

In the camera 11 of the seventh embodiment, in the subroutine"Photographing Operation" at Step S1125 in the main routine, thesubroutine "Photographing Operation" shown in FIGS. 47 and 48 in thecamera 11 of the fifth embodiment is performed. Furthermore, in thecamera 11 of the seventh embodiment, in the subroutine "Subject DistanceMeasuring Operation" at Step S1207, the subroutine "Subject DistanceMeasuring Operation" shown in FIGS. 49 and 50 in the camera 11 of thefifth embodiment is performed. Still furthermore, in the camera 11 ofthe seventh embodiment, in the subroutines "Measuring Area SettingOperation" at Step S1315, "Data Correcting Operation" at Step S1319,"Sensor Correcting Operation" in the "Data Correcting Operation" at StepS1319 and "Sensor Correcting Operation" in the "Data CorrectingOperation" at Step S1319, the corresponding subroutines in the camera 11of the fifth embodiment are respectively performed.

Still furthermore, in the camera 11 of the seventh embodiment, in thesubroutine "Interpolation Arithmetic Operation" at Step S1321, thesubroutine "Interpolation Arithmetic Operation" shown in FIG. 61 in thecamera of the sixth embodiment is performed.

Still furthermore, in the camera 11 of the seventh embodiment, in thesubroutine "Default Check Operation" at Step S617 in the subroutine"Interpolation Arithmetic Operation" at Step S1321, the subroutine"Default Check Operation" shown in FIG. 62 in the camera of the sixthembodiment is performed.

In the camera 11 of the seventh embodiment, in the subroutine "SubjectImage Distance Value Calculating and Selecting Operation" at Step S1325,the subroutine "Subject Image Distance Value Calculating and SelectingOperation" shown in FIG. 64 which is unique to the seventh embodiment ofthe present invention is operated. This subroutine shown in FIG. 64 willbe hereinafter discussed.

In this subroutine "Subject Image Distance Value Calculating andSelecting Operation", two threshold values (i.e., two reliabilityjudgement levels) are set, one having a first reliability judgementlevel "A" and the other having a second reliability judgement level "B"smaller than the first reliability judgement level "A". Each judgementlevel determines whether a subject image distance value is valid orinvalid. In the case where even one subject image distance value greaterthan the first reliability judgement level "A" can not be obtained, oneor more than one subject image distance value greater than the secondpredetermined value "B" is selected. Subsequently, among these values,i.e., those values greater than "B" but less than "A", the greatestsubject image distance value is selected as an optimum calculatedsubject image distance value to be used in the focusing operation.

The aforementioned two threshold values, i.e., the first and secondreliability judgement levels are each determined in accordance with thedegree of inclination of the above mentioned two straight lines, betweenwhich the real minimum value of the evaluation function is considered tolie. It has been already mentioned before that the steeper the twostraight lines are, the more precisely the center position "x" of asubject image formed on a light receiving area on a line sensor can bedetected.

When the control enters the subroutine "Subject Image Distance ValueCalculating and Selecting Operation" shown in FIG. 64, the order oflight receiving areas for each of which a subject image distance valuecalculation is to be performed is determined at Step S701, andthereafter, a subject image distance value is calculated in a subroutinelabelled "Subject Image Distance Value Calculating Operation" at StepS703. Thereafter, the control proceeds to Step S704. At Step S704 it ischecked whether the "Subject Image Distance Value Calculating Operation"subroutine of Step S703 has completed for all the light receiving areasMC, MLC, MRC, ML and MR. The control proceeds to Step S707 if it isjudged at Step S704 that the "Subject Image Distance Value CalculatingOperation" subroutine has completed for all the light receiving areas,or returns to Step S701 if not.

At Step S707, the reference reliability judgement level "L" is set atthe first level "A", and thereafter, the control proceeds to asubroutine labelled "Maximum Value Selecting Operation" at Step S709. AtStep S709 the maximum value "max" is selected from among all the subjectimage distance values greater than the first level "A", at Step S709.

After Step S709 the control proceeds to Step S711 to check if themaximum value "max" selected at Step S709 is greater than "0" (zero). Ifthe maximum value "max" is greater than "0", the control proceeds toStep S721. At Step S721 the maximum value "max" is set as a subjectimage distance value or data, to be used in a focusing operation.

If it is judged at Step S711 that the maximum value "max" is equal to orsmaller than "0", or there is no subject image distance value greaterthan the first level "A", the control proceeds to Step S713.

At Step S713, the reference reliability judgement level "L" is set atthe second level "B", and thereafter, the control proceeds to asubroutine labelled "Maximum Value Selecting Operation" at Step S715.This subroutine is similar to one at Step S709.

At Step S715, the maximum value "max" is selected from among all thesubject image distance values greater than the second level "B". AfterStep S715 the control proceeds to Step S717 to check if the maximumvalue "max" selected at Step S715 is greater than "0" (zero). If themaximum value "max" is greater than "0", the control proceeds to StepS721, where the maximum value "max" is set as a subject image distancevalue or data, to be used in a focusing operation.

If it is judged at Step S717 that the maximum value is equal to orsmaller than "0" the control proceeds to Step S719 where an error bit,which indicates there is no valid subject image distance value, is set.Thereafter, the control proceeds to Step S721, and subsequently, thecontrol returns.

It will be appreciated that a subject image distance value of highreliability can be obtained through the operations of Steps S707, S709,S711 and S721, and that the subject image distance value can be obtainedwith less strict limits through the operations of Steps S711, S713, S715and S717.

The subroutine "Maximum Value Selecting Operation" at Step S709 or StepS715 will be hereinafter discussed with reference to the flow chart ofFIG. 65.

When the control enters this subroutine, firstly, the maximum value isset "0" (zero). Thereafter, the operations of Steps S733 through S745are performed for all of the light receiving areas MC, MLC, MRC, ML andMR.

At Step S733 the absolute value of the inclination of one of thestraight lines shown in FIG. 57 is calculated, using the followingformula:

    R.sub.1 =|y.sub.1 -y.sub.0 |/|x.sub.1 -x.sub.0 |

wherein "R₁ " represents the absolute value of the inclination of one ofthe straight lines shown in FIG. 57. Subsequently, at Step S735 theabsolute value of the inclination of the other straight line shown inFIG. 57 is calculated, using the following formula:

    R.sub.2 =|y.sub.3 -y.sub.2 |/|x.sub.3 -x.sub.2 |

wherein "R₂ " represents the absolute value of the inclination of theother straight line shown in FIG. 57.

Thereafter, at Step S737, the smaller of the two calculated absolutevalues R₁ and R₂ is set as a reliability value "R", and subsequently,the control proceeds to Step S739. Here the reliability value "R" iscompared with the reference reliability judgement level "L" so as tojudge whether the reliability value "R" is valid or invalid.

At Step S739, if the reliability value "R" is smaller than the referencereliability judgement level "L", the control proceeds to Step S741. Ifthe reliability value "R" is equal to or greater than the referencereliability judgement level "L", the control proceeds to Step S745.

At Step S741, it is checked if the subject image distance value for alight receiving area is greater than the maximum value "max", and thecontrol proceeds to Step S743 if this is the case.

At Step S743, the maximum value "max" is set equal to the subject imagedistance value.

At Step S741 if it is judged that the subject image distance value for alight receiving area is equal to or smaller than the maximum value"max", the control proceeds to Step S745.

At Step S745, it is checked whether or not the operation of Steps S733through S743 has been performed for all the light receiving areas MC,MLC, MRC, ML and MR. The control returns to Step S733 if the operationof Steps S733 through S743 has not been performed for all of the lightreceiving areas, or the control returns if the operation of Steps S733through S743 has been performed for all the light receiving areas.

Note that the reference reliability judgement level "L" is the firstlevel "A" when the subroutine "Maximum Value Selecting Operation" shownin FIG. 65 is called at Step S709 and that the reference reliabilityjudgement level "L" is the second level "B", smaller than the firstlevel "A", when the subroutine "Maximum Value Selecting Operation" shownin FIG. 65 is called at Step S715.

As is understood from the foregoing, according to the seventh embodimentof the present invention, a precise subject image distance value can beobtained since it is selected from among all the subject image distancevalues greater than the first reliability judgement level "A".Furthermore, the chance of a state occurring in which focus isimpossible decreases, since a subject image distance value is selectedfrom among all the subject image distance values greater than the secondreliability judgement level "B", smaller than the first reliabilityjudgement level "A", when any subject image distance value greater thanthe first reliability judgement level "A" cannot be obtained.

Moreover, according to the seventh embodiment of the present invention,since it is judged if a calculated subject distance value is valid orinvalid in accordance with the inclination of correlative evaluationdata, the calculated subject distance value of a low contrast can beremoved without checking the contrast of a subject image.

In the seventh embodiment, although two threshold values or reliabilityjudgement levels are set so as to judge if a calculated subject distancevalue is valid or invalid, more than two reliability judgement levelsmay be set to judge the same.

Furthermore, in the seventh embodiment, although the number of lightreceiving areas for each line sensor is five, the number may be lessthan or more than five. The arrangement of those light receiving areason each line sensor may also be any other arrangement. Stillfurthermore, although the maximum value "max" is set equal to the valueof the calculated subject image distance value, it could be set at anyvalue.

Another embodiment (i.e., an eighth embodiment) of a camera to which adistance measuring apparatus according to an eighth aspect of thepresent invention is applied will be discussed below. The camera of theeighth embodiment is similar to the camera of the fifth embodiment towhich the fifth aspect of the present invention is applied, except inseveral respects. Since much of the structure of the eighth embodimentis similar to the fifth embodiment, the following explanation will onlybe directed to that structure unique to the eighth embodiment. Thecamera of the eighth embodiment will be explained below with referenceto FIGS. 35˜38, 46˜49, 66˜71.

FIG. 66 shows a relationship between the light receiving areas used fora multiple measurement and the line sensors in the eighth embodiment ofthe present invention. According to the camera of the eighth aspect ofthe present invention there are three light receiving areas, namely, acentral light receiving area MC and left and right light receiving areasML and MR. The left and right light receiving areas ML and MR arepositioned on the left and right sides of the central light receivingarea MC, respectively (FIG. 67). Light receiving areas MC, ML and MR ofthe line sensors 153L and 153R correspond to respective subject lightreceivable ranges mc, ml and mr. The line sensors 153L and 153R are eachprovided with 128 photodiodes which serve as light receiving means. Eachlight receiving area contains 36 consecutive photodiodes.

The operation of the camera of the eighth embodiment will be hereinafterdiscussed. The main routine performed by the CPU 131 is the same as thatof the camera of the fifth embodiment which is shown in FIG. 46.

The subroutine "Photographing Operation" at Step S1125 in the mainroutine is also the same as that in the camera of the fifth embodimentwhich is shown in FIGS. 47 and 48.

The subroutine "Subject Distance Measuring Operation" at Step S1207 inthe camera of the eighth embodiment will be discussed below withreference to FIGS. 49, 50 and 68.

The subroutine "Subject Distance Measuring Operation" in the camera ofthe eighth embodiment is identical to that of the camera of the fifthembodiment (shown in FIGS. 49 and 50), except that the former subroutineincludes the operations at Steps S1360 and S1362 between Steps S1313 andS1315 whereas the latter subroutine does not include the same betweenSteps S1313 and S1315 (FIG. 50). The following explanation of thesubroutine "Subject Distance Measuring Operation" in the camera ofeighth embodiment, will only be directed to those steps unique to theeighth embodiment, i.e., Steps S1360 and S1362.

After the distance measuring unit 151 is reset at Step S1313, it ischecked at Step S1360 whether or not the variable "i" is "0"(zero). Thecontrol proceeds to a subroutine labelled "Sub-Photometering Operation"at Step S1362 if the variable "i" is "0"(zero), or to Step S1315 if not.When the control first enters this subroutine "Subject DistanceMeasuring Operation", the control proceeds to Step S1362 since thevariable "i" is "0"(zero). On or after the control enters thissubroutine for the second time, the control proceeds to Step S1315,without performing the subroutine at Step S1362. In the subroutine atStep S1362, regarding either the line sensor 153L or 153R, a firstsub-photometer value (i.e., the difference between the maximumbrightness value and the average brightness value) and a secondsub-photometer value (i.e., the intermediate value among threedifferences, that is, the difference between the average brightnessvalue of the light receiving area MC and that of the light receivingarea ML, the difference between the average brightness value of the islight receiving area MC and that of the light receiving area MR and thedifference between the average brightness value of the light receivingarea MR and that of the light receiving area ML) are calculated.

The operations at Steps S1315 through S1321 are performed for each ofall the three light receiving areas MC, ML and MR.

After the subject image distance value has been calculated for each ofall the three light receiving areas MC, ML and MR, the control proceedsto the subroutine "Subject Image Distance Value Calculating andSelecting Operation" at Step S1325. At Step S1325, one of the threecalculated subject image distance values is selected, to be used for afocusing operation.

The subroutine "Distance Measuring Unit Reset Operation" at Step S1313in the eighth embodiment of the present invention will be discussed withreference to a flow chart shown in FIG. 69. In this subroutine shown inFIG. 69, each circuit in the distance measuring unit 151, a memory(e.g., RAM) etc., are all reset to start the integral operation of thedistance measuring unit 151. Furthermore, in this subroutine, areference brightness value BvS₀ (i.e., the maximum brightness value) iscalculated.

When the control enters the subroutine "Distance Measuring Unit ResetOperation" at Step S1313, a reference brightness value measuring timerstarts at Step S801, and subsequently, the distance measuring unit 151is reset at Step S803, i.e., the electric charges of each line sensor153L, 153R are swept or output to start the integral operation of thedistance measuring unit 151.

Subsequently, the control proceeds to Step S805, and further proceeds toStep S807 at the time the integral value of any light receiving elementfirst reaches a constant value, or re-enters Step S805 until theintegral value of any light receiving element first reaches the constantvalue. When the integral value of any light receiving element firstreaches the constant value, the controller 155 outputs a referenceintegral end signal to the CPU 131. When the CPU 131 receives thereference integral end signal, the CPU 131 makes the referencebrightness value measuring timer stop (Step S807), and subsequently,calculates the aforementioned reference brightness value BvS₀ (StepS809) in accordance with the time necessary for the firstly-reachedintegral value to reach the constant value and a predetermined datatable (not shown) showing the corresponding relation between theintegral operation time and the brightness value.

The subroutine "Sub-Photometering Operation" at Step S1362 in the eighthembodiment of the present invention will be discussed with reference toa flow chart shown in FIG. 70. This subroutine shown in FIG. 70 is tocalculate the data necessary for judging whether or not a backlit-stateexists, in accordance with the subject image data detected by distancemeasuring unit 151.

When the control enters this subroutine shown in FIG. 70, all thesubject image data of either the line sensor 153L or 153R are input tothe CPU 131 at Step S851, and subsequently, the average brightness value(i.e., average intensity value) of all the input subject image data(i.e., average brightness value "A") is calculated at Step S853.Thereafter, at Step S855, the difference between the average brightnessvalue "A" and the reference brightness value BvS₀ having been calculatedat Step S809 is calculated and set as the first sub-photometer value.

Thereafter, at Step S857, the average brightness value of all thesubject image data outputted from the light receiving elements in thelight receiving area MC is calculated and set as a sub-averagebrightness value AC.

Likewise, at Step S859, the average brightness value of all the subjectimage data outputted from the light receiving elements in the lightreceiving area MR is calculated and set as a sub-average brightnessvalue AR.

Likewise, at Step S861, the average brightness value of all the subjectimage data outputted from the light receiving elements in the lightreceiving area ML is calculated and set as a sub-average brightnessvalue AL.

Thereafter, at Step S863, the absolute values of the differences betweenthe sub-average brightness values AC and AL, between the sub-averagebrightness values AC and AR, and between the sub-average brightnessvalues AR and AL are calculated and set as the absolute values D(1),D(2) and D(3), respectively. Thereafter, at Step S865, the calculatedabsolute values D(1), D(2) and D(3) are arranged in order of magnitude.Subsequently, at Step S867, the intermediate absolute value D(1), D(2)or D(3) is selected and set as the second sub-photometer value.

The subroutine "AE Calculating Operation" at Step S1211 in the eighthembodiment of the present invention will be discussed with reference toa flow chart shown in FIG. 71. In this subroutine shown in FIG. 71, itis judged whether or not a backlit-state exists, using theaforementioned first and second sub-photometer values calculated at thesubroutine "Sub-Photometering Operation" at Step S1362.

When the control enters this subroutine, predetermined first and secondbacklit-state judging values Lv1 and Lv2 are set at Step S901.Thereafter, at Step S903, the difference between the main photometervalue obtained through the photometering circuit 137 and the firstsub-photometer value is calculated and set as a first brightnessdifference S1.

Thereafter, it is checked at Step S905 if the first brightnessdifference S1 is greater than the first backlit-state judging value Lv1,and the control proceeds to Step S907 if this is the case, or proceedsto Step S911 if this is not the case. When it is judged at Step S905that the first brightness difference S1 is greater than the firstbacklit-state judging value Lv1, it can be judged that a backlit-stateexists, thus the strobe circuit 143 is turned ON to prepare for a strobeemission at Step S907, and furthermore, at Step S909, a brightness valuecorrection amount Δ bv is calculated according to the followingequation:

    Δbv=S1-L1

wherein "L1" represents a first predetermined exposure value (e.g., 1.5Ev in this embodiment).

Conversely, when it is judged at Step S905 that the first brightnessdifference S1 is equal to or smaller than the first backlit-statejudging value Lv1, it can be judged that a backlit-state does not exist,thus the control proceeds to Step S911, without carrying out theoperations at Steps S907 and S909.

At Step S911, it is checked if the second sub-photometer value isgreater than the second backlit-state judging value Lv2, and the controlproceeds to Step S913 if greater, or to Step S919 if the secondsub-photometer value is equal to or smaller than the secondbacklit-state judging value Lv2.

When greater at Step S913, the strobe circuit 143 is turned ON toprepare for a strobe emission at Step S913, and subsequently, it ischecked at Step S915 if the brightness value correction amount Δ bv issmaller than the difference between the second sub-photometer value anda second predetermined exposure value L2 (i.e., 1.5 Ev in thisembodiment), and the control proceeds to Step S917 if that is the case,or to Step S919 if the brightness value correction amount Δ bv is equalto or greater than the difference between the second sub-photometervalue and the second predetermined exposure value L2.

At Step S917 the brightness value correction amount Δ bv is set as thedifference between the second sub-photometer value and the secondpredetermined exposure value L2.

It will be accordingly appreciated that the smaller one between the twodifferences, i.e., the difference between the first brightnessdifference S1 and the first predetermined exposure value L1 and thedifference between the second sub-photometer value and the secondpredetermined exposure value L2, is adopted as the brightness valuecorrection amount Δ bv to be used for exposure value correction.

In the operations at Steps S911 through S917, it is checked if thesecond sub-photometer value is greater than the second backlit-statejudging value Lv2, the strobe circuit 143 is turned ON if that is thecase, and the difference between the second sub-photometer value and thesecond backlit-state judging value Lv2 is replaced by the brightnessvalue correction amount Δ bv if the difference is smaller than thefirstly set brightness value correction amount Δ bv.

At Step S919, in the case where the brightness value correction amount Δbv obtained at Step S909 or S917 is over a predetermined amount, e.g.,over +3 Ev or -3 Ev, the brightness value correction amount Δ bv isadjusted to be the predetermined amount, e.g., +3 Ev or -3 Ev,respectively.

After Step S919, at Step S921, the subject brightness value Bv iscorrected by subtracting the brightness value correction amount Δ bvfrom the main photometer value (i.e., the subject brightness value Bv).Thereafter, at Step S923, the AE data is calculated, using the correctedsubject brightness value Bv and the input ISO speed value Sv, so as toobtain an optimum time value (shutter speed) Tv and aperture value Av.Thereafter, an AE data limiting operation is performed at Step S925 inwhich the time value Tv and aperture value Av obtained at Step S923 areadjusted so as to fall within respective limit values predetermined inaccordance with the capacity or ability of camera's shutter and aperturein the case where the time value Tv and aperture value Av are over therespective limit values. After Step S925 the control returns.

In the subroutine "AE Calculating Operation" shown in FIG. 71, althoughboth operations, i.e., the operation in which the strobe circuit 143 isturned ON and the operation in which an exposure value is adjusted for abacklit-state, are both performed, only one of them may be performed.

As can be seen from the foregoing, according to the eighth aspect of thepresent invention, the distance measuring unit 151 also functions as abacklit-state detecting apparatus to detect a backlit-state. Therefore,it is not necessary to provide a plurality of photosensors or asplit-type photosensor used exclusively for detecting a backlit-state.

In the eighth embodiment of the present invention, although each linesensor 153L or 153R is provided with three light receiving areas MC, MLand MR, more than three light receiving areas may be provided. In orderto detect a backlit-state, it is preferable that two light receivingareas, used for detecting a backlit-state and respectively located onthe right side of the center light receiving is area and the left sidethereof, be located apart from the center light receiving area by as faras possible.

In the aforementioned fourth through eighth embodiments of the presentinvention, although the corresponding aspect of the present invention isapplied to the distance measuring unit provided in a lens-shutter typecompact camera, it may also be applied to the distance measuring unitprovided in an SLR camera.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

We claim:
 1. A distance measuring apparatus of a camera, comprising:apair of image forming lenses, each of said image forming lenses forminga subject image; a pair of line sensors on which said subject images arerespectively formed through said pair of image forming lenses, whereineach line sensor has a plurality of light receiving elements, each lightreceiving element converting received light into an electrical signalrepresenting a brightness value, so that subject distances of differentareas of a common subject image can be measured in accordance with saidconverted electrical signals; a photometering circuit that detects anaverage brightness value of said common subject image; and a judgingsystem that evaluates whether a backlit-state exists bv detecting amaximum brightness value from all said brightness values, calculating anaverage brightness value from said brightness values for one of saidpair of line sensors, calculating a first difference between saidmaximum brightness value and said average brightness value, comparingsaid first difference with a first predetermined reference value anddetermining that said backlit-state exists when said first difference isgreater than said first predetermined reference value.
 2. The distancemeasuring apparatus of claim 1, wherein said judging system furthercalculates a sub-average brightness value from said brightness valuesfor each of said different areas, calculates a first difference betweena first one of said sub-average brightness values and a second one ofsaid sub-average brightness values, calculates a second differencebetween said first one of said sub-average brightness values and a thirdone of said sub-average brightness values and calculates a thirddifference between said third one of said sub-average brightness valuesand said second one of said sub-average brightness values, selects anintermediate value from among absolute values of said first, second andthird differences, compares said intermediate value with a secondpredetermined reference value and determines that said backlit-stateexists in the case where said intermediate value is greater than saidsecond predetermined reference value.
 3. The distance measuringapparatus of claim 1, further comprising a distance measuring unitprovided in a camera, said distance measuring unit including said pairof image forming lenses and said pair of line sensors.
 4. A camerahaving a distance measuring apparatus, said camera comprising:a pair ofimage forming lenses in said distance measuring apparatus each imageforming lens forming a subject image; and a pair of line sensors in saiddistance measuring apparatus on which said subject images arerespectively formed through said pair of image forming lenses, whereineach line sensor has a plurality of light receiving elements, each lightreceiving element when actuated converting received light into anelectrical signal representing a brightness value, so that subjectdistances of different areas of a common subject image can be measuredin accordance with said converted electrical signals; a photometeringcircuit that detects an average brightness value of said common subjectimage; and a judging system that evaluates whether a backlit-stateexists by detecting a maximum brightness value from all said brightnessvalues, calculating an average brightness value from said brightnessvalues for one of said pair of line sensors, calculating a firstdifference between said maximum brightness value and said averagebrightness value, comparing said first difference with a firstpredetermined reference value and determining that said backlit-stateexists when said first difference is greater than said firstpredetermined reference value.
 5. The camera of claim 4, furthercomprising a strobe, wherein said judging system actuates said strobe toprepare for emitting light when determining that said backlit-stateexists.
 6. The camera of claim 4, wherein said judging system correctsan aperture value in accordance with said first difference whendetermining that said backlit-state exists.
 7. The camera of claim 4,wherein said judging system further calculates a sub-average brightnessvalue of said brightness values for each of said different areas,calculates a first difference between a first one of said sub-averagebrightness values and a second one of said sub-average brightnessvalues, calculates a second difference between said first one of saidsub-average brightness values and a third one of said sub-averagebrightness values and calculates a third difference between said thirdone of said sub-average brightness values and said second one of saidsub-average brightness values, selects an intermediate value from amongabsolute values of said first, second and third differences, comparessaid intermediate value with a second predetermined reference value anddetermines that said backlit-state exists when said intermediate valueis greater than said second predetermined reference value.
 8. The cameraof claim 7, further comprising a strobe, wherein said judging systemactuates said strobe to prepare for emitting light when evaluating thatsaid backlit-state exists.
 9. The camera of claim 7, wherein saidjudging system corrects an aperture value in accordance with said firstdifference when evaluating that said backlit-state exists.
 10. Thecamera of claim 7, further comprising a distance measuring unit, saiddistance measuring unit including said pair of image forming lenses andsaid pair of line sensors.